Normally, Iceman is one of the most personable and light-hearted of the X-Men. In the core Marvel Universe, he was one of the first X-Men, recruited by Charles Xavier to lead the future of mutant-kind. He's proven himself to be a dependable and heroic young man, embracing his Omega-Mutant status as one of Earth's most powerful mutants as well as his own status as an openly gay man. But in the reality known as the Age of Apocalypse, Iceman ended up on a far more brutal and devious figure.
The Age of Apocalypse was caused by the time-hopping intervention of Charles Xavier's son, Legion. Legion ventured into the past and tried to assassinate Magneto before he could ever become a threat. However, Xavier threw himself in front of the blast, saving his friend at the cost of his own life. This battle radically altered the trajectory of the Marvel Universe by awakening Apocalypse decades earlier and prompting him to begin his war on humanity long before the world would have been strong enough to fight back. In this new and brutal timeline, many of the mutants who would become heroes were instead ruthless champions of Apocalypses' regime, while a handful -- led by Magneto -- stood in defiance as the X-Men.
Among the most powerful was Iceman, who was still one of the earliest X-Men. However, Magneto had no patience for Iceman's light-hearted side. Magneto pushed him to grow up and fully utilize his powers from the onset. This resulted in an Iceman who was far more powerful than his contemporary self from Earth-616 -- but also one who had developed a grim view of the world. Rarely reverting to his human form, this version of Iceman proved how adaptable his powers could be. As a living streak of ice, he could create copies of himself and more or less teleport -- merging with any body of water and reforming his body miles away in seconds. He had such a level of control over this power that he could even possess other people and restore them to their regular bodies afterward.
Over the years, Iceman remained a determined member of the X-Men with no restraint towards killing. He took part in the final battle against Apocalypse and was part of the reconstruction of his world alongside the other surviving X-Men who lived to see an age without Apocalypse. He was one of the most prominent X-Men who remained powerful enough to fight against Weapon X (the Wolverine of this world) after he was corrupted and transformed into a new variant of Apocalypse by the Celestial Death Seed. He became particularly close with his fellow X-Man Nightcrawler -- but one fateful battle changed everything.
Exhausted with his life, Iceman made a dangerous deal when the Uncanny X-Force visited the Age of Apocalypse during the Dark Angel Saga by betraying his allies and siding with Dark Beast. Coming to be known as the Sinister Iceman, this version of Bobby Drake fought against X-Force and their allies as one of Dark Angel's champions. The Sinister Iceman was one of the few survivors of the battle from their side, escaping into Earth-616 only after helping ensure the deaths of his former teammates Sunfire and Wildchild. Enraged at his betrayal, the AOA version of Nightcrawler remained behind to hunt him down.
Joining X-Force for a time, Nightcrawler ended up hunting down the Sinister Iceman in Madripoor in Uncanny X-Force #24 by Rick Remender and Phil Noto. Confronting him, Nightcrawler was able to drag his former friend and teammate into a fiery furnace room, where the intense heat helped counteract his natural mutant abilities. Beating Iceman down with his bare fists, Nightcrawler ultimately killed the Sinister Iceman by forcing him headfirst into the furnace, burning him alive. Perhaps the darkest version of Iceman in the multiverse, the Sinister Iceman is a tragic and ultimately grim take on one of the most iconic X-Men.