The (first?) end of Apocalypse
While he managed to transform one of the X-men, Angel, into his horseman War, Apocalypse’s habit of declaring victory through loss led him to abandon his suborned Celestial starship to X-Factor as a trap. They eventually made friends with it, using it as their base for some time before Apocalypse once again attacked and in one of his most successful, infamous schemes, kidnapped Cyclops’ son, Nathan Christopher Summers, and infected him a with a techno-organic virus as part of some twisted experiment.
Needless to say, Scott Summers was pissed, and with the help of Jean Grey, destroyed Apocalypse, supposedly for good, but like many, if not most, characters in the X-Men franchise, death was only a minor inconvenience.
