Krakoa, The Island That Walks Like A Man, is a central part of the Dawn of X's new mutant status quo, providing a homeland equipped to host and help mutants and X-Men all over the globe and solar system. The island has played a significant role in X-Men canon for decades and undergone multiple retcons and backstory changes.
With such a lengthy and convoluted history, here are the most important aspects of Krakoa to remember.
Nuclear Origin
The first Krakoa origin story marked it as a landmass that gained sentience after becoming a nuclear testing site, making it a major product of its time. The name itself came from the infamous Indonesian volcano Krakatoa, a significant part of the 1960s and '70s cultural and scientific zeitgeist.
A more sinister influence came from the US military's use of Pacific islands as nuclear test sites, devastating them and any lifeforms not removed beforehand. Unlike these real life counterparts, Krakoa and its surviving biosphere were 'mutated' by the radiation and became a complex organism with more or less human levels of intelligence.
A 2018 stand-alone comic by writer Dennis "Hopeless" Hallum and artist Djibril Morisette-Phan, Journey Into Mystery: The Birth of Krakoa, showed the painful origin of the island's sentience and its innate dislike of humanity a few decades before its chronological debut in Giant Size X-Men #1 (1975).
In Giant Size X-Men, the original X-Men were captured by Krakoa after they landed on it in search of a strong mutant energy signature. Cyclops was the only one to escape, as the wiley island could feed on mutant energy and thought he would bring even more mutants back for a rescue attempt. This led to the recruitment of iconic X-Men Storm, Wolverine and Nightcrawler as part of a new team, which successfully managed to free the others.
In the ensuing fight, the island created a physical form that communicated with the mutants verbally and telepathically in a rather cheesy villain monologue. The day was finally saved when Polaris used her electromagnetic powers to launch the entire island into the stratosphere, where it remained for some time.
Deadly Genesis Retcon
Over the next few decades, Krakoa only appeared in flashbacks or partial cameos, such as a sample Emma Frost used to create a "Danger Grotto" for her mutant students to train in. One such appearance in 2006's Deadly Genesis storyline was so important it radically changed almost everything known about the island, as well as much of what the X-Men knew about their own history.
In this series written by Ed Brubaker and penciled by Trevor Hairsine, a surge of energy from M-Day caused a chunk of Krakoa to fall back to Earth.
After the X-Men investigated it and were attacked by a mysterious young mutant who had been trapped inside, a series of events led to Professor X confessing to yet another violation of his former students' trust: Before the events of Giant Size X-Men, he had worked with Moira MacTaggert to assemble another team of young mutants to rescue the original X-Men from Krakoa. They only managed to free Cyclops, who was shocked to discover that one of the new young X-Men was his long lost brother, Gabriel Summers.
Scott could barely process this before the young mutants were cut down before his eyes as he was flying back to Westchester. To keep Cyclops from falling apart, the professor telepathically altered his memories and removed any knowledge of the other team and his brother, who had actually managed to survive -- with the aid of his teammate Darwin -- in energy form until he was freed.
To maintain his deception, Professor X not only altered Cyclops's memories of Krakoa and his escape, but telepathically kept the other X-Men from seeing the island as it truly was. Krakoa was actually mindless and incapable of planning or communication, much less purposefully releasing Cyclops to bring more mutants back -- let alone spewing villainous monologues.
Okkara Origin
Dawn of X changed and updated many aspects of Krakoa's biology and abilities, so it's not too surprising that it was given a new origin as well.
In Powers of X #4, Doug Ramsay, the only person capable of directly communicating with the island (it doesn't have the speech or intelligence seen in Giant Size X-Men, but it definitely has a mind and a language of its own) learned Krakoa had originally been part of a larger continent called Okkara. At some point, an unknown enemy used the Twilight Sword to split Okkara into two islands -- Krakoa and Arrako -- and released a demonic army from the chasm.
According to Krakoa, the army was stopped by the ancient mutant Apocalypse when he cast the army and the island Arrako into the chasm and sealing it, leaving his Horsemen to guard it. Krakoa knew Apocalypse had done it for the greater good of the world, but still mourned for its missing half.
Not only is this new origin story vastly different from the original, it also has the potential to become a major plot point in the future. The army and the bearer of the mysterious Twilight Sword could very well still be waiting in the sealed chasm for a chance to invade the surface world, along with Arrako. Depending on what happens next, the two islands may even get the chance to reunite into Okkara -- a reunion which has the potential to radically alter the new mutant nation, if only on a geographical level.