BIOGRAPHY
In 1945, the island of Krakoa in the Pacific was exposed to immense levels of radiation. A nuclear bomb dropped by the U.S. military impacted Krakoa and caused a radical change in the surrounding area. The entire ecosystem of the island mutated to possess a hive mind and a burgeoning, sentient intelligence. Nick Fury and the Howling Commandos happened to be flying near the test site and crashed on Krakoa as a result of the explosion. They were severely affected by the lingering radiation and the aggressive growth of Krakoa. Fury made contact with the telepathic core of Krakoa and made peace with the island. In exchange for Krakoa absorbing the radiation from the Howlers and the area, Fury lied to his superiors about what they experienced on the island. This led the Army to believe the bomb was a dud, and Krakoa's existence remained a secret from everyone. [Journey into Mystery: The Birth of Krakoa #1]
Decades later, Krakoa registered on the X-Men's Cerebro mutant detection system as one massively-powerful mutant, and they traveled to the island in order to locate that mutant. Once they arrived in the Strato-Jet, however, the X-Men were confronted by Krakoa as it assumed a gargantuan humanoid form. They also found they were unable to reach out telepathically to Xavier, and were overpowered. The island felt the X-Men's mutant energies were pleasing and began feeding off of their lifeforces. [Giant-Size X-Men #1]
Charles Xavier gathered a second team of X-Men, quickly trained with a telepathic crash course in tactics and the use of their mutant powers. At Krakoa, Vulcan and his team fought through 
Krakoa's avatars and managed to locate Cyclops being drained by the living island. Unfortunately, the entire team was unknowingly being weakened by Krakoa ambiently feeding off of their energy. Having been drained the most, Cyclops piloted the Strato-Jet up into the sky, trying to get past the telepathic masking field Krakoa seemed to be generating. Vulcan and the others insisted on remaining behind to search for the remaining X-Men. To his horror, Scott witnessed one of Krakoa's volcanic avatars seemingly murder Vulcan's entire team before his eyes. (In fact, only Sway and Petra were killed outright. Vulcan and Darwin were horribly injured and entombed deep beneath the surface of Krakoa.)
Helpless and distraught, he returned to New York to tell Professor Xavier what had happened. Vulcan had been Cyclops' brother, which only further contributed to his sense of failure and despair. Needing Cyclops in fighting condition, Professor X decided to edit his memories of the encounter. He removed all knowledge of Vulcan and his team from Scott's mind, making Cyclops believe the island had let him go for unexplained reasons. [X-Men: Deadly Genesis #4-6]
Professor Xavier assembled a new team of X-Men. When Cyclops returned to Krakoa with these recruits, the X-Men split up to survey the island. Krakoa assailed them with strangling vines, malicious avalanches, mutated birds and giant crustaceans that were all part of its hive mind. Still, the X-Men fought their way to the temple where the original X-Men were being drained. Once Cyclops had his friends and teammates removed from Krakoa's grip, the living island finally 
revealed itself as the mutant they were searching for. In its colossal, humanoid form, Krakoa struck out at the X-Men. At the direction of Professor Xavier, the X-Men combined their abilities, with Storm and Lorna Dane upsetting the island's electromagnetic field while Cyclops and Havok fed them even more power. Eventually, Krakoa was cut loose from the planet's gravitational pull, hurtling out into orbit where it would hopefully never menace the X-Men again. [Giant-Size X-Men #1] Xavier furthered his deception of the team during these events, making them believe Krakoa was fully sentient and malevolent. The X-Men "heard" Krakoa telepathically relate its origins and the plan it hatched to release Cyclops in order for him to bring back more mutants to feed upon. [X-Men: Deadly Genesis #6]
The Stranger was a vastly-powerful cosmic being of enigmatic origins, known for studying and experimenting on creatures he found interesting and unique. Having visited Earth several times in 
the past, the Stranger discovered Krakoa in space near Earth and brought the living island back to his Laboratory World for further study. Quasar of the Avengers briefly encountered Krakoa on the Laboratory World while pursuing Over-Mind and the Squadron Supreme. Many of the Stranger's lab subjects escaped during this incident, but Krakoa's fate is unrevealed. The Stranger's Laboratory World remains the last known location of the original Krakoa. [Quasar #14-15]
Krakoa did not depart for the Stranger's Laboratory World in its entirety, however. Some of Krakoa's land mass remained in Earth's orbit, including the chunk of rock containing Vulcan's team of X-Men. When the Decimation removed enormous amounts of mutant energy from the planet, that energy passed through Krakoa, reawakening Vulcan and Darwin in space. [X-Men: Deadly Genesis #1] Furthermore, spores from the living island had previously fallen back to Earth as Krakoa was being ejected from the atmosphere. One such spore incubated on another island in the South Pacific, growing to full sentience over time. Having witnessed the dramatic confrontation between Krakoa and the X-Men, the native people of that island came to see the X-Men as gods. The self-styled Son of Krakoa needed the occasional life essence to sustain his growth, and maneuvered the islanders into performing human sacrifice, sending helpless victims down deep into the earth for him to feed on.
The Son of Krakoa was far more openly megalomaniacal than his sire. He perceived himself as a new form of life ready to supplant the human race, a Vega-Superior even more powerful than 
Homo-Superior. When happenstance led one of his father's murderers, the X-Men / Excalibur member Nightcrawler, to crash on his island, he intervened on one of the sacrifices. The Son of Krakoa confronted Nightcrawler with his Vega-Men, using doppelgangers of Cyclops, Wolverine, Colossus, Angel and Nightcrawler himself to attack. Nightcrawler eventually defeated the Son of Krakoa by tricking him into chasing Kurt out into the sea, separating him from the island that fed his bio-matter and kept him alive. [Excalibur (1st series) #31]
Perhaps unwisely, some of Krakoa's bio-matter was also used at the Massachusetts Academy when it became the new home for Xavier's School for Gifted Youngsters. Instead of a traditional 
holographic Danger Room, Sean Cassidy and Emma Frost opted to train the students of Generation X in a bio-sphere, or "Danger Grotto" as Jubilee called it. Presumably, the unique nature of Krakoa's bio-matter allowed them to reshape the landscape and environment through artificial means, customizing the bio-sphere for different training scenarios. [Generation X (1st series) #1]
An undercurrent of menace existed in the bio-sphere for many months. A wraith-like creature known as a Token manifested there. [Wolverine (2nd series) #94] Black Tom Cassidy and his creation Mondo attacked Generation X in part through manipulating the bio-sphere. In fact, Tom and Mondo's own plant-based abilities seemed to integrate with the bio-sphere in ways that were never fully explained. Tom incapacitated Generation X using energy-leeching vines exactly like those had Krakoa used on Banshee's original team, and somehow transported Generation X through the Earth until their vegetation pod resurfaced in the Pacific Ocean at the exact location the island of Krakoa once rested. [Generation X (1st series) #25]
The bio-sphere eventually disappeared entirely, apparently being transplanted through dimensions to arrive near some distant and alien cityscape. Forge and Banshee hypothesized that Krakoa still existed somewhere out there in the universe, and was attempted to reconstitute itself and all of its lost or displaced matter. This certainly seemed like bad news for the X-Men, but nothing ever came of these ominous events. [Generation X (1st series) #44, 47]
Other examples of Krakoa bio-matter continued to surface around the globe. Sunspot and Moonstar's young X-Men training team discovered another living island with Krakoa's aggressive tendencies. Whether it was a second living ecosystem created in the same atomic blast as Krakoa or another spore that fell to Earth after the original evacuated from the planet is unknown. [Young X-Men #7] A geneticist named Kaga stole research from Hank McCoy and used it to create Bio-Sentinels from mutant and other DNA. Among his creations were a combination of Krakoa and Brood genetic material. [Astonishing X-Men (3rd series) #33]
Mister Sinister also experimented in reproducing Krakoa for his own purposes. He created a Sinister London underneath Alaska, complete with a castle carved onto the back of his cloned Krakoa. The mobile castle was destroyed during Sinister's confrontation with the Phoenix Five. [Uncanny X-Men (2nd series) #14-17]
Maximilian von Katzenburgen of the Hellfire Club also took an interest in Krakoa development. He used an artificial super-garden to cultivate his own Krakoa bio-matter and implanted it in the grounds of the Jean Grey School for Higher Learning. Once Krakoa had taken root, he was able to control the entity using an electromagnetic leash which forced it to obey. Krakoa attacked the X-Men as the school opened, causing seismic damage to the area and forging avatars of earth and stone to fight the mutants.
The student Quentin Quire was able to reach out to Krakoa, however. Kid Omega's telepathic charisma won over the artificial lifeform, convincing it to see itself as a mutant and join forces with the X-Men. With the electromagnetic leash severed as well, Krakoa became an honorary member 
of the X-Men. [Wolverine and the X-Men (1st series) #1-3] By inhabiting and animating the grounds of the Jean Grey School, Krakoa became a part of everyday life for the X-Men. He formed a relationship with the groundskeeper, Toad, but could also be won over by students with bags of fertilizer. On the flip side, Hellion learned a valuable lesson about not urinating on the flowerbeds. Krakoa could also literally grow diamonds from trees, helping the school with its constant cash flow problems. He welcomed new students like Dust to the school once Cyclops' Utopia island closed down. [Wolverine and the X-Men (1st series) #4, 8, 15]
The Hellfire Club and their Hellfire Academy began to openly target members of the Jean Grey School. They recruited staff like Husk and Toad and the students Oya, Broo, Kid Omega and Glob Herman. Beast and Rachel Grey reached out to Krakoa to find where the Academy might be hiding their kids. Krakoa agreed to help and separated from the school grounds for the first time, becoming an enormous and independent humanoid. He transported the X-Men to an archipelago where von Katzenburgen had grown other Krakoas in defense of the Hellfire Academy. Krakoa proved to be superior to his brethren, fighting victoriously alongside a giant ice avatar Iceman against the Hellfire Krakoas. [Wolverine and the X-Men (1st series) #33-35]
Toad's allegiance to the Hellfire Academy was due to his feelings for Husk and he ultimately helped Kid Omega and the others escape. The X-Men still felt they couldn't trust him, however, and he was let go as the groundskeeper. Krakoa had a tearful good-bye with Toad as he left the Jean Grey School. Krakoa settled back into the school grounds, acting as defender of the school whenever it was threatened by super-villains, time traveler, or other dangers. [Wolverine and the X-Men (1st series) #38-42, (2nd series) #1-3]
As the Terrigen Mists caused the M-Pox plague to overtake mutants worldwide, the X-Mansion was moved to the dimension of Limbo where it acted as X-Haven. Krakoa was not part of the displacement, and moved his bio-matter offshore to function as an independent island in the Pacific Ocean. He spent time with Kid Omega for a while before Quire decided to return to the X-
Men when they established the Xavier Institute for Mutant Education and Outreach in the heart of Central Park. However, he neglected to look in on Krakoa, causing the living island to seek Quentin out. By tunneling through Manhattan bedrock to reach Quire, Krakoa inadvertently caused massive property damage in New York City, forcing the X-Men to intervene. Kid Omega was blamed for not keeping Krakoa under better control and he quit the school, taking Krakoa with him. [Generation X (2nd series) #8-9]
Krakoa set himself up as a deserted island and Quentin settled in to sulk for a while. He was contacted by his former classmate Kid Gladiator for an encounter with the Phoenix. Later, Jubilee reached out to Quire at Krakoa and invited him back to the school. Kid Omega returned to help his friends against M-Plate, once again leaving Krakoa behind. One can only hope Quire keeps better tabs on Krakoa this time, because New York City doesn't seem interested in having Central Park as a permanent living land mass. [Mighty Thor (2nd series) #18, Generation X (1st series) #85-86]