Introduction
Some may think that Charles Xavier’s only adventures were after he founded the X-Men, but the truth is he already led an interesting and eventful life before his mutant pupils came around. One such occasion was when he and his stepbrother, Cain Marko, fought in a Korean police action. Cain had decided to run away from his duties as a soldier of the United States army and Charles Xavier followed his sibling to try and convince him of the error of his ways. The two brothers accidentally entered a hidden temple, which was the resting place of the Gem of Cyttorak. 
Cain grabbed the red, glowing jewel and, not taking the time to understand the strange inscription, he read it aloud, "Whosoever touches this gem shall possess the power of the crimson bands of Cyttorak! Henceforth, you who read these words shall become forevermore a human Juggernaut!" and instantly began his transformation into the unstoppable Juggernaut, granting Cain Marko sheer unlimited physical power.
Description / Capabilities
What is this Gem of Cyttorak that it can change a human being to such degree? Apparently, it is a magical artifact, somehow linked to a deity called Cyttorak. Over the years, artists’ interpretations of the gem have varied. It has been shown in different shapes (spherical, flat and oval, six-cornered) and sizes (from as large as a basketball to a softball). The only thing that remained is the glowing, red color. Even the name changed from writer to writer - Ruby of Cyttorak, Gem of Cyttorak, Crimson Crystal of Cyttorak and a number of other slight variants. In this article, the term "Gem of Cyttorak" will be used, as that seems to be a more generic term that would fit both a ruby and a crystal.
Now, what does the Gem of Cyttorak do? Its incredible energies can cause anyone that comes in contact with it to transform into Cyttorak’s Exemplar, the Juggernaut, a literally, unstoppable individual. The Juggernaut possesses immense strength and stamina, and doesn’t have the need to eat or breathe. The single weak spot is the Juggernaut’s mind but, to shield him from any mental attacks, his armor’s helmet is shielded to psychic attacks. On one occasion after the gem returned from a trip through space, it seemed that it grew new capabilities, as it was then used by a young boy. Despite touching the Gem, the boy was not physically changed but gained the power to shoot beams of concussion force, animate wax statues and to send communication signals around the globe. Whatever became of that is unknown, but the Gem’s status has clearly changed, as afterwards it was infused to Cain Marko’s body.
Also important to know is that there exists a world within the Gem of Cyttorak, the so-called Crimson Cosmos. Several people have travelled to and from this strange dimension, where time doesn’t move. You can learn more about the place here.
Origin
Over a thousand years ago, eight beings of magical power gathered together, their names being Balthak, Cyttorak, Farallah, Ikonn, Krakkan, Raggadorr, Valtorr and Watoomb. In their meeting, they began to argue over whose power was the greatest. It is not known who, but one of them suggested that they make a wager that would be known as the Wager of Octessence. 
Each of these eight beings were to make a totem that held a fraction of its creator’s vast powers and the artifacts would turn the first human who touched it into an Exemplar, the living embodiment of that power. All of the entities used outside agents to build temples that housed their totems. In Cyttorak’s case, he tricked an order of monks into building his temple in an area that, in modern day, belongs to Korea. A certain spell was to ensure that, once one of the totems had been touched, other humans would be drawn to the other seven locations, starting the Octessence. Each Exemplar would lead one eighth of Earth‘s population into battle, until only one of them remained. [Iron Man (3rd series) #22]
Ancient History – the past centuries
However, centuries passed without any of the totems being touched and some of the temples fell prey to the forces of nature. They were buried in earthquakes, flooded by the ocean or overgrown with vegetation. Cyttorak’s temple in Korea, though, was one of the few exceptions.
During his travels, the Ancient One happened to reach the temple and curiously ventured inside. Knowing of the ruby’s enchantment, he had no intention of touching the Gem of Cyttorak. He only wanted to observe and learn. Still, his presence alerted Xorak, the temple’s guardian. At some point in history, Cyttorak had been banished from Earth but created this being to safeguard his temple and destroy everyone who entered. He was no match for the Ancient One, though, who magically banished Xorak to the Crimson Cosmos within the gem. [X-Men (1st series) #33]
In another century, a group of heretic monks tried to harness Cyttorak’s power for themselves, but they failed and, instead, only called forth the most destructive aspect of this being of immense power. Sadly for the rebel monks, this entity murdered them all and the nearby villagers, and the threat would have continued to spread if not for two magicians. Despite being rivals, Gomurr the Impetuous and Tar the Initiate of the Ebon Vein worked together and were successful in forcing the entity into his own totem, the magical Gem of Cyttorak. Thus, it now had a dual nature: it served as a prison for Cyttorak, but likewise it would transform a human into his Exemplar. Neither one of the rival magicians trusted the other enough to guard the ruby, fearing they might succumb to the lure of phenomenal power, so they placed the Gem of Cyttorak once more in the temple and sealed its entrance under a mountain of rocks. [X-Men Unlimited (1st series) #12]
Chronology – the recent years
Even though the cave had been lost, Cyttorak still managed to find an avatar for his powers. Before Cain Marko became the infamous wielder of the gem, another man by the name of Jin Taiko had used it. Jin was a member of the village near Cyttorak’s temple. He served Cyttorak for decades until he fell out of favor with Cyttorak when he refused to destroy his own village, which had begun worshipping another god. Cyttorak began looking for another avatar and one soon came along when Cain Marko and Charles Xavier stumbled upon the ruins of the temple. Apparently, the entrance to the cave had been reopened by explosions and bombings, right in time for the two stepbrothers to happen upon it. Reading the hieroglyphics on the wall, Xavier recognized the warnings of the gem’s enchantment, but Cain would not listen to his hated stepbrother. Instead, he picked up the jewel, instantly transforming himself with the curse of Cyttorak.
As the transformation occurred, the already unstable temple began to collapse, due to the seismic events transpiring without. The Communists that were searching for the two lost soldier-brothers had caught up with them and were shelling their would-be hiding place. Xavier escaped the collapsing building in time and walked away, wondering whether his brother had managed to escape as well. Cain’s fate was still uncertain, though, as he had to also contend with the previous avatar of Cyttorak. Both men possessed a portion of the power and were forced to fight to the death to claim the full title of the Juggernaut. Cain eventually won by snapping his opponent’s neck but unfortunately he was now trapped beneath tones of solid rock. Still, that was not enough to stop the unstoppable Juggernaut. Though he needed about ten years, he eventually dug himself out, while the Gem remained in the ruins. [X-Men (1st series) #12, New Excalibur #14-15]
While attempting to use a special machine to purge his stepbrother of the Juggernaut powers, Charles Xavier was hit by an energy feedback and rendered comatose. While the Juggernaut escaped with some of Xavier’s mental power, the X-Men asked Dr. Strange for help, who told them that they needed the prototype gem. In order to get that artifact, he spirited Cyclops and Marvel Girl to Korea, where they cleared the cave entrance of the debris and then ventured inside the temple. Mesmerized by the Gem of Cyttorak’s beauty, Jean almost touched it, but her lover stopped her in time. The couple chanted an incantation of Dr. Strange, which took them inside to the Crimson Cosmos, from which they successfully retrieved the prototype gem. Rejoining their comrades, the X-Men used this second gem to cure Xavier and also to defeat the Juggernaut. When he saw the similarly looking gem, he wanted it for himself but, when he touched it, he and the prototype gem were both sucked into the Crimson Cosmos. [X-Men (1st series) #32-33] It took him quite some time and several unsuccessful attempts before he could fully return.
Back on Earth, Cain Marko formed a close partnership with Black Tom Cassidy and they would often battle their opponents together for the following months and years. 
Shortly before Black Tom’s birthday, the Juggernaut had an idea for what would make for a rather unique birthday present and went to Korea to retrieve the Gem that gave him his powers. He entered the temple with ease and got what he came for, the Korean army standing in his way not even slowing him down. When Tom opened the gift and touched the glowing gem, he was transformed into another Juggernaut. However, both of them had only half of the original’s powers. Black Tom didn’t like this one bit and engaged his ally in a brief battle, which was then interrupted by Spider-Man and the X-Men. Rogue leeched off Cassidy’s Juggernaut powers and, later, Cain Marko reclaimed the full set when he touched the ruby a second time. Realizing that the ruby was not only the source of his strength but could also be used to take away from him, the Juggernaut decided to hurl it into space, where nobody could use it. [Marvel Team-Up (1st series) #150]
However, fate had something different in store for the magical artifact. Following her master, Galactus, to Earth’s orbit, Nova accidentally bumped into the Gem of Cyttorak and sent it back to the planet, where it was found by a boy named Stevie, who picked it up, though was not transformed. Instead, Stevie could use the gem in unexpected ways, from animating wax statues to sending a communication signal halfway around the continent. He even managed to release concussive force blasts that held the Juggernaut at bay. [Avengers West Coast #64]
It is unknown what really became of Stevie but, apparently, Cain Marko encountered the child a second time and successfully reclaimed his power source, as it somehow became infused to his body. Whatever the case, the Juggernaut soon found yet another ruby he wanted to claim for himself. When Dr. Strange and Nova found themselves trapped in the Crimson Cosmos by a manifestation of Cyttorak, the sorceror summoned Cain Marko to help them. Cyttorak seemed to be an elf-like figure, who wore a pointed helmet-like hat with a ruby grafted onto it. Thinking that this new stone would increase his own abilities, the Juggernaut battled his benefactor and ripped the stone out. Strangely, though, he felt no difference. Additionally, when the two heroes teamed up against him and forced him drop the glowing jewel, it returned to its rightful place. [Dr. Strange (3rd series) #44]
The Gem didn’t show up again until Cain Marko was captured by Onslaught and the near-omnipotent entity ripped the Gem from the chest of the magical Juggernaut. The shock of Cain Marko was not that he could be defeated, but that any being on the planet could rip the infused Gem from his body. Even worse, Onslaught imprisoned Cain Marko in the Crimson Cosmos inside the Gem of Cyttorak and, continuing his charade of being the still harmless Professor Xavier, used the Gem of Cyttorak as a paperweight. [X-Men (2nd series) #54, Onslaught: X-Men]
Not much later, Stephen Strange sensed the abandoned Gem and travelled in his astral form to the desk of Charles Xavier to examine the magical item. Using his magical senses, Strange recalled the events that transpired and realized that Cain was trapped in the Gem. However, before he could act, Gomurr and Tar both ventured to the Crimson Cosmos and empowered Cain Marko, allowing him to defeat Cyttorak. Afterward, they all returned to Earth, the Gem again being bonded to the Juggernaut. [X-Men Unlimited (1st series) #12]
Many months later, charlatans tried to steal the Juggernaut’s power by using a fake gem, with the resemblance of the Gem of Cyttorak. Never having been the brightest one, Cain was easily tricked into believing the new gem could double his powers. Actually, once he arrived at the place of the strange cult, they drained his powers away from him. The Juggernaut was severely weakened, if not dying, and if not for three of the X-Men stealing the fake gem and handing it to Black Tom, he might have died. [Uncanny X-Men (1st series) #361]
Over a decade after Cain Marko had become the Juggernaut, finally the Wager of the Octessence was triggered when one of the other seven totems transformed an unsuspecting human into an Exemplar. Now the trigger spell worked and, one by one, each of the ancient totems called out to a nearby human until each of the eight magical entities had its representative. The Exemplars met on the North Pole, where they started building a God-Machine that would have removed the willpower from all humans across the globe to make them loyal servants of the eight armies. However, having had years to adjust to the transformation, the Juggernaut’s will was not as overwhelmed by the entity he represented, enabling him to fought back and was able to stop the Ceremony of the Octessence from occurring. [The Eighth Day crossover] 
For his betrayal, the other Exemplars wanted to punish the Juggernaut, but the Avengers intervened. At first hopelessly outmatched, the heroes managed to get through to some of the newly-born villains and, disagreeing with each other, the Exemplars let go of their plan and departed. [Avengers (3rd series) #24-25]
An encounter with the entity Prosh was to change Cain’s life and his outlook on it forever. Prosh sent Cain, along with some other mutants on a mission to the past. Cain’s mind was transported to an earlier version of himself but during the journey he stopped off at numerous points in his life. He realized that for too much of his life he had been trapped either under rubble, in prison or in a situation he couldn’t get out of. When his mission was over, he decided to change his ways and accepted a job from the Commission on Superhuman Activity. [X-Men Forever (1st series) #1-6]
Cain’s heroic actions weren’t to last, however, and after a fight with Cyclops, Cain and Black Tom went back to Cassidy Keep. Cain noted that his powers were beginning to weaken as a result of Cyttorak’s displeasure with him. 
When Black Tom’s new secondary mutation went out of control, Cain called upon the X-Men to help. Cain nearly died saving the X-Men in an ensuing battle but was saved by a young boy named Sammy. Deciding once again to mend his ways, Cain joined the X-Men at the invitation of Xavier. Over the next few months, Cain mellowed out a lot and even struck up a friendship with a young boy named Sammy. Cyttorak was becoming tired of Cain and so he gave a portion of his power to a young boy, who subsequently challenged Cain for the title of Juggernaut. Cain beat his rival but he still remained on the heroic path. [Uncanny X-Men (1st series) #410-412, 421-422, 429, 432-436]
What became of the new Juggernaut is unknown but most likely he was stripped of his power, given that Cain later wielded the full power of the gem again. Cain returned to the X-Men and resumed active duty. His newfound attitude was put to the ultimate test when Sammy, having discovered Black Tom was going to attack the X-Men, was murdered by the villain. A fight ensued between the X-Men and Black Tom’s gang, which resulted in them getting sucked into another dimension, Cain included. [X-Men (2nd series) #161-164]
Though Cain would somehow return to join the British team New Excalibur, he still only possessed a portion of his original strength. When he was defeated yet again in battle, he decided to do something about it. He travelled to Korea to the temple where he first became the Juggernaut. Cyttorak was waiting for him there but, when Cain went to take hold of the gem, the deity denied him access to it. Instead, he revealed that Cain was never the first choice to become the Juggernaut, Xavier was. 
However, it had been Cain who had picked up the gem and, for a while, his anger and ruthlessness had served Cyttorak well. Now, with Cain’s calmer demeanor and his unwillingness to cause destruction, he decided to seek out a new Juggernaut. Cyttorak brought forward a new candidate who had been partially empowered with his the gem. Cain and this new Juggernaut fought until Cain had gained the upper hand. He was about to deliver the killing blow when his New Excalibur teammates found him. Ashamed by what he was about to do, Cain stopped and let the other man live. Even though he didn’t kill the man, Cyttorak still allowed Cain to claim the gem, possibly because he saw that Cain still possessed the rage that had long consumed him. Cain rejoined his team but decided to keep the fact he was now in possession of the gem a secret from anyone else. [New Excalibur #13-15]
When the Hulk attacked the Xavier Institute looking for Xavier, the X-Men sent out distress calls to all their allies. New Excalibur answered but, as they were the other side of the world, they couldn’t help. 
Cain, however, decided he could. He used the gem to contact Cyttorak and bargained with him to send him to the Institute. In return, he would truly become the Juggernaut again. Cyttorak obliged and Cain was teleported to the school where he immediately engaged the Hulk in combat. However, Cain still didn’t possess the strength he once did and was no match for the Hulk. When he wondered why he wasn’t at full strength, Cyttorak answered through the gem and said that it wasn’t his doing, it was Cain’s. Cain was holding back because he was denying himself that he was Cyttorak’s avatar. Cain claimed that he wanted to destroy but Cyttorak corrected him and said the reason he had come was to help Xavier. Cyttorak made Cain see that to possess the full strength of the Juggernaut he would have to embrace the Juggernaut and all he stood for. Cain fought the Hulk again but this time he held his own. Ultimately, he was defeated by the Hulk but Cain was a changed man regardless. He decided to embrace Cyttorak and left the X-Men and New Excalibur and warned off anyone who would track him down. [World War Hulk: X-Men #2-3]
Whilst the gem itself remained hidden, its influence on Cain waned as Cyttorak became more and more displeased with him. Cain was possessed first by the Uni-Force and then by an ancient Asgardian Serpent entity. When the opportunity to claim a new avatar came along, Cyttorak jumped at the chance and empowered Colossus into being his new Juggernaut. Unfortunately, that did not work out either, as Magik eventually purged the gem’s influence from her brother and Cyttorak was once again left without an avatar.
A Gem of Cyttorak did appear on Earth a short while later but it turned out it was from an alternate universe. Cain’s old Thunderbolt team had need of his immense power and so Satana opened up a portal to a world where Cain had died and Cyttorak was without an avatar. Once Cain had completed his task, though, the gem was sent back to the world from which it had come. [Dark Avengers (2nd series) #182-183]
A while later, the real gem appeared back on Earth in the ancient Korean temple, where it was soon discovered by a group of armed men. Drawn to its power, they went to grab it but were killed by a demonic creature Cyttorak had left there to guard it. Cyttorak then sent out a call across the world to all those worthy of wielding his power, including Cain and Colossus. With the X-Men aware of the gem’s existence again, they travelled to the temple, without Colossus, to deal with the situation. They found the guardian and engaged it in battle but were surprised to see Crossbones, Man-Killer and an assassin named Jinn there. Whilst Rockslide fought the demon, the X-Men attacked the potential future Juggernauts. From within his dimension, Cyttorak watched the chaos with anticipation but his eyes were firmly set on an as-yet unknown candidate. As the fight progressed, both Colossus and Cain joined the fray, hell-bent on getting to the gem before anyone else. The demonic guardian was defeated and many of those whom Cyttorak had called were also dispatched. Though Cain had gotten to the gem in the meantime, he was stopped from touching it by Colossus. The two men fought but quickly realized they neither wanted to claim the power; they wanted to prevent anyone else from doing so.
Unbeknownst to them, the mysterious man who had gone unnoticed slipped into the chamber and took hold of the gem. Cyttorak was pleased and he granted this man, the Living Monolith, his power, turning him into the new Juggernaut. The Living Monolith grew as tall as a skyscraper and proceeded to wreak havoc on the surrounding area as the X-Men looked on in horror. After a quick brainstorming session, they decided to confront Cyttorak directly and so Pixie teleported Cain, Colossus and Rachel Grey into the Crimson Cosmos. They called Cyttorak’s bluff and told him that humanity would never worship him the way he wanted and that there was only one inevitable outcome.
Colossus stepped forward and asked Cyttorak to grant him his full power, so that he could show the god what unstoppable truly meant by fighting and killing him. Cyttorak gladly accepted but altered the terms of the agreement before anyone could protest. The Living Monolith was stripped of the Juggernaut power and Cain was given it all, returning him to the mantle of the Juggernaut once more. Cain attacked the X-Men and nearly beat them, but Colossus managed to knock him into the sea and bury him under a landslide. [Amazing X-Men (2nd series) #15-19]
With Cain in control of the gem again, it remains to be seen if he has learned from any of his past mistakes or whether he will make a series of new ones.