Almost 200 years old, Nathaniel Essex is a scientist at heart. He was inspired by Charles Darwin’s 19th century research into evolution and the origins of man. He took Darwin’s theories a step farther, positing that the offspring of man will mutate, becoming something superhuman. He called this the “Essex Factor.” He was mocked for this theory, and losing a son did not help his increasingly obsessive mental state. Shown that his theories were correct by the appearance of time-travelling X-Men, Cyclops and Jean Grey, he became even further obsessed with the idea of mutants. He took too kidnapping and experimenting upon live humans with no care or consideration for their safety and wellbeing. He even experimented upon the corpse of his dead son. He encountered En Sabah Nur (Apocalypse), who gave him his powers and immortality. Since then, he has been continuing with his experiments. He even went as far as working with the Nazis during World War II. Over time, Mister Sinister’s obsession has turned towards self-improvement, no longer concerned with sharing his knowledge for the benefit of the world at large. In the present, he has become a powerful and merciless foe for the X-Men. He was responsible for ordering the Marauders to hunt down and exterminate the Morlocks (see Sabretooth’s entry on the list). He is a ruthless man incapable of empathy, and he will never cease his pursuit of unlocking the potentials of the mutant gene.