BIOGRAPHY - Page 7
While the Thunderbolts were out, the Asgardian God of Fear, the Serpent, unleashed seven hammers on the planet to seek out and empower minions as "the Worthy." 
One hammer crashed into the Raft, causing serious damage. Juggernaut found the hammer and fell victim to the Serpent's influence exacerbating his fears. It was said that the power of Cyttorak would have given Cain the ability to resist the hammer's control if he had wanted, but his fears led Cain to willingly submit to the Serpent. He was reborn as Kuurth, Breaker of Stone. Kuurth / Juggernaut then split open the Raft with one strike from his new hammer, and flew off to spread the Serpent's message of fear. [Fear Itself #2, Thunderbolts (1st series) #158]
When Kuurth landed in the Midwest and began advancing on the city of Chicago, the Thunderbolts reasoned that Marko may still be active and fighting inside his mind, since he didn't travel all the way to the city by air. The T-Bolts tried to reach Cain and / or divert him from the path of innocent lives, but the Juggernaut had now been made unstoppable by two different gods. Satana attempted to spiritually link the Thunderbolts to Cain, but they were driven out of Cain's mind by the spiritual avatar of Kuurth. Still, they must have reached something inside him, and Kuurth used his hammer to fly off, abandoning Chicago to advance on another city. [Thunderbolts (1st series) #159-161]
On the roads leading to San Francisco, Kuurth landed and used the Serpent's power to create an acolyte of destruction. He enchanted a gas station attendant to act as the Voice of Fear, a crier to spread the gospel of the Serpent as Juggernaut advanced upon the city and its "sinful haven" of mutants. Whether through magic or fear alone, a mob of followers soon fell into line behind Kuurth as he marched on San Francisco, leaving the blazing sigil of the Serpent on the ground in his wake. Cyclops and X-Men coordinated with Mayor Sinclair to prevent 
Juggernaut from damaging the city or its populace, but they failed time and time again. Juggernaut's slow but unstoppable advance on the city was designed to increase the fear and dread among his intended victims, as his Voice lay down an ultimatum: the mutants or the humans would be spared, if only they destroyed the other group for the Serpent.
The X-Men consulted their magical expert, Illyana Rasputin, who concluded Cyttorak might take umbrage to his avatar spreading fear for another deity. She traveled to the Crimson Cosmos and confronted Cyttorak with Juggernaut's "infidelity." Cyttorak acted as she expected and removed the power of the Juggernaut from Cain Marko, choosing a new avatar in Illyana's brother, Colossus. Colossus was unleashed upon Kuurth and the magically-enhanced mutant proved to be more unstoppable than the Serpent's weakened Worthy. The Serpent recalled Kuurth from his march on San Francisco before the new Juggernaut completely destroyed him. [Uncanny X-Men (1st series) #540-543] Even without the power of Cyttorak, Cain remained active as Kuurth until the final battle with Odin and Iron Man's enchanted Avengers, "the Mighty," over Asgard in Oklahoma. When the Serpent was defeated, the power of his hammers left the Worthy, and Cain reverted back to a fully normal human being. [Fear Itself #6-7]
Cain Marko resigned himself to prison after that, returning to the Raft as a normal inmate. The Thunderbolts had been lost in time since the Serpent War, leading FACT to assemble a new, more suspicious crew of Thunderbolts comprised of Norman Osborn's former Dark Avengers. Luke Cage and the remaining Thunderbolts eventually learned FACT was violating international law by trying to confiscate an alien power source from the rogue nation of Sharazad. 
The Thunderbolts returned from the future, having seen the apocalyptic consequences of FACT and the Dark Avengers' meddling. Ghost coordinated with Warden Walker to have Cain Marko furloughed from the Raft and brought to Sharazad where Cage and the T-Bolts were trying to contain the threat. With the help of the Man-Thing, they located a dimension where Cyttorak existed but the local Cain Marko had died. As Cain reached through the Man-Thing's dimensional gateway, the power of the other Cyttorak flowed to him, restoring his powers as the Juggernaut.
Juggernaut broke through Sharazad's defenses, gaining access to the power source and letting Cage and the T-Bolts stop the Dark Avengers from devastating a sizeable portion of the Earth. As the temporary charge of Cyttorak power began to fade, Marko reconnected with Luke Cage, who apologized for benching him before the Serpent War. Cage acknowledged he knew about Marko's 
fear of imprisonment and was wrong to use it against him. As the Thunderbolts transported back to the Raft, Man-Thing chose not to "phase in" the remaining criminal members of the T-Bolts. Although they were returning to a life as criminals and fugitives, Marko and the Thunderbolts amicably parted ways with their former captors and supervisors. At the Nexus of All Realities in the Everglades, Man-Thing gave each Thunderbolt a portal to where they desired. Cain left through his gateway, finding open desert with plenty of room to run, perfect for his sentiments. [Dark Avengers (2nd series) #180-183]
Marko remained in retirement for many months. He built a farm in Utah and lived there in peace, planting a field of flowers in defiance to all the devastation he had caused in the past. However, Colossus lost the power of the Juggernaut in the meantime and Cyttorak soon became restless again. He demanded a new avatar and sent out a psychic call heard by those suitable to be his vessel, drawing them to his rebuilt temple in Southeast Asia. Marko sensed the call as well and vowed to prevent Cyttorak's return. Presumably through his old mercenary contacts, Cain acquired the equipment he needed and the service of a teleporter, Vanisher, to get him to Asia.
When Cain materialized in the temple, the X-Men were already on scene defending the gem against prospective Juggernauts. Nightcrawler thought to embrace Marko as a friend, but Cain had heard of Charles Xavier's death and blamed the X-Men for it. It seemed Cain finally realized too late that his step-brother was one of the few people to give a damn about him, and wanted to strike out at his students for failing to protect him. Fighting his way to the center chamber, Cain confronted his fellow former avatar, Colossus. Each mistaken about why the other was there, Marko and Rasputin fought to stop each other from reclaiming the gem, when both actually wanted to destroy it. They were distracted with each other long enough for Ahmet Abdol to claim the gem, transforming the Living Monolith into the new, 800 foot tall human Juggernaut.
The X-Men were barely able to slow this combined version of two of their most powerful foes. Colossus invoked the name of Cyttorak to get himself and Marko to appear before the demon-god in the Crimson Cosmos. 
Colossus then manipulated Cyttorak into admitting that what he really wanted was a challenger, someone powerful enough to match and kill him. The X-Man offered to take on the mantle of the Juggernaut again. Cyttorak accepted the bargain, but not the players, and made Marko his Juggernaut once again. More powerful than ever before, missing his classic weaknesses, Cain was truly a human Juggernaut. Colossus was able to temporarily sink the Juggernaut off the coast of Southeast Asia, but Cain Marko will inevitably return. [Amazing X-Men (2nd series) #16-19]
Driven for years by his hatred of his step-brother Charles Xavier, the Juggernaut fought his students the X-Men to get at Charles. The roles have been altered, for the Juggernaut now seeks to destroy the X-Men on behalf of his step-brother, whose death he puts at their feet. The reasons don't matter, though. Vengeance, whatever its flavor, has always been nothing more than an excuse for Cain Marko to relish in the power of being an unstoppable human Juggernaut.