MISTER SINISTER

Mister Sinister was first mentioned by Sabretooth in Uncanny X-Men (1st series) #212, and Psylocke picked up a shadowy mental image of him in #213. However, he did not make an actual physical appearance before #221.

Sinister's real name was revealed in the AoA, but confirmed in our reality in X-Men Annual 1995. Sinister impersonated Apocalypse during the X-Cutioner's Song to command his Horsemen.

Mister Sinister was believed dead in X-Factor (1st series) #39 when Cyclops apparently blew him apart, starting the long-running misconception that Mister Sinister was invincible except for Scott's optic blasts. This concept even made it into the 1990's animated series. Sinister returned in X-Factor (1st series) #72-75, revealing his death was a ruse. He deliberately took a point blank blast from Cyclops's eyes in X-Men (2nd series) #23 to prove he was impervious to the effect.

Although X-Factor (3rd series) #27 showed Sinister's corpse, New X-Men (2nd series) #46 was the issue that showed his death. Sinister attempted to survive his death in X-Men: Legacy and X-23 by planting his consciousness into one of several bodies, before eventually succeeding and returning in Uncanny X-Men (1st series) #544.

It was revealed in Gambit (3rd series) #13-14 that Sinister's morphing abilities were derived from a time-traveling mutant named Courier, whose genetic material Essex extrapolated and applied to his own body. In Powers of X #4, we learned that Sinister's physical strength and power were derived from John Proudstar. Powers of X also coined the term "Chimera mutant" for Sinister and other mutants he might create based on multiple genetic templates merged as one.