Dr. Nathaniel Essex, also known as Mister Sinister, is a fictional character and supervillain appearing in American comic books published by Marvel. He is a Victorian England scientist who was inspired by the work of his contemporary Charles Darwin and becomes obsessed with engineering humanity into a perfect race of superhumans. As he learns about mutants (superhuman beings born with the X-gene), Essex encounters the mutant villain Apocalypse. The two become allies and Apocalypse uses alien Celestial technology to transform the British scientist into Mr. Sinister, an ageless man with superpowers. Later on, Sinister increases his power through self-experimentation. In the modern-day, Sinister develops a great, but obsessive interest and protective attitude towards the mutant heroes Cyclops and Jean Grey, believing their DNA can create the ultimate mutant, making him a recurring foe of the X-Men.