6. Mr. Sinister
In Victorian London, Apocalypse meets Nathaniel Essex, a British scientist who teaches him more about the genetic differences which make him a mutant. After transforming Essex into Mister Sinister, the two strike up a partnership, although a betrayal by the mad scientist isn’t too far down the line at this point. You see, Sinister’s main obsession is the Summers’ bloodline (Summers, as in Cyclops and Havok) and he even at one point clones Jean Grey, who becomes impregnated and whose child is sent into the future.
Famously, Sinister is also responsible for the massacre of the underground mutants known as the Marauders.