Krakoa is a fictional character in Marvel Comics, commonly associated with the X-Men. It is a living island, a sentient ecosystem able to command all the living things native to its island body, and even its terrain. Its name was derived from the real Indonesian volcano island Krakatoa.
Although Krakoa has made only one notable appearance in the X-Men franchise, it is vividly remembered by the fanbase as the main enemy in what may be the most influential X-Men comic of all time, Giant-Size X-Men #1. Krakoa is directly responsible for the formation of the "new" X-Men.
In Giant-Size X-Men #1, the X-Men (then consisting of Cyclops, Angel, Havok, Iceman, Marvel Girl (Jean Grey), and Polaris) came to the island after Cerebro detected an unknown mutant there, and were captured by Krakoa, who used them as foodsources. Cyclops was the only one able to flee, but doesn't remember what happened. Professor X decides to recruit international mutants to save his X-Men, namely Colossus, Nightcrawler, Storm, Sunfire, Thunderbird, Banshee, and Wolverine, and sends them to Krakoa.
Cyclops' group of mutants pair off and after each pair encounter and defeat various aspects of the island, the new X-Men team finds the original X-Men, who are weakened from being fed upon by Krakoa for so long. At this point, it is revealed that the island is itself the mutant they had originally detected and Krakoa battles the new and old X-Men by forming a giant humanoid body out of its terrain. With a combination of psi interference by Professor X and energy blasts from Cyclops and Havok, Storm is able to supercharge Polaris' magnetic powers with bolts of lightning. Polaris interacts with the Earth's core and creates a magnetic pulse so strong that she is able to launch Krakoa into outer space. The X-Men - now counting thirteen members - are saved.
Later a "son of Krakoa" appeared in Excalibur #31, the result of a spore that was released from Krakoa as it was shot into space. Nightcrawler eventually defeated this "Vega-Superior" by tricking him into drowning himself.
Krakoa was apparently found and captured for study by the cosmic entity known as The Stranger, as seen when Quasar visited one of his 'laboratory worlds'. Krakoa was eventually freed as well as many of the specimens.
The 2006 X-Men: Deadly Genesis storyline features a major retcon in which it is revealed that many of the elements in Giant-Size X-Men #1 were in fact deceptions and delusions created by Professor X to hide the major part of the story. Another team of young mutants, composed of Petra, Darwin, Sway, and the third Summers brother Kid Vulcan, from a parallel X-Mansion led by Moira MacTaggert, were sent to help the original X-Men. They managed to save Cyclops and returned him to Professor X. However Krakoa, no more intelligent than an animal, killed Petra and Sway and left Darwin and Kid Vulcan almost dead. Xavier had erased all records of the real events in Cyclops' mind, and altered the mutants' minds to cast the illusion of a speaking, sentient Krakoa.
In the Ultimate Marvel continuity of Ultimate X-Men, Krakoa was reimagined as an apparently normal island near Genosha, on which TV mogul Mojo Adams hosts his gruesome reality TV show Hunt for Justice, in which mutant felons are hunted to death. It is where Ultimate Deadpool takes Spider-Man and the X-Men in the Deadpool arc of USM.What If? Deadly Genesis, Vulcan and his team make their way through the island, surviving its assault. Vulcan becomes separated from the group and finds the captured X-Men. After accidentally killing them all in a panic, Vulcan escapes the temple and, with the rest of his team, the island itself. Krakoa is then jettisoned into deep space, where it remains untouched for years until being discovered by the Silver Surfer. There, Sway finds a time pocket and uses her powers to replay the events of Vulcan's killings. After confronting and disabling him of his powers, Professor Xavier banishes Vulcan to the island, where he is forced, as punishment, to replay the transpired murders of the X-Men every time he requires food.
In the story What If? Rise and Fall of the Shi'ar Empire Krakoa is resurrected by a power-mad Vulcan using the Phoenix Force, with a battle between him, Rachel Summers, Havok, Cyclops, and Cable taking place on it.