Mr. Sinister was originally Dr. Nathaniel Essex, a doctor who was from Victorian London. He was married to Rebecca Grey, of Grey Hall, and was a friend of James Xavier, the family physician. Rebecca had a serious illness, which Xavier's treatments could not cure. Essex was upset that he was forbidden from treating his own wife, as it would have been considered an impropriety in Victorian times. He ran the local asylum for the physically infirm.
Essex became obsessed with the works of Charles Darwin, particularly the Theory of Natural Selection. Believing that humanity had removed themselves from the processes of natural selection, he felt that it was time for man to experience a giant evolutionary leap. He began to do his own research into genetic mutations in humans, particularly those that caused apparently supernatural abilities (such as production of a low-level magnetic field). However, when he presented his findings to Darwin, he was dismissed as a quack. He became ever more obsessed. He collected mutants in his asylum and performed "sinister" and painful experiments on them. He also experimented on himself, which granted himself superhuman abilities (including instantaneous healing, among others), and on his wife Rebecca (in secret), and cured her of her affliction.
When James Xavier went to see his friend, Xavier discovered Essex's monstrous experiments, and released the poor people that were locked away. Essex was driven away by an angry mob. He attempted to take Rebecca with him, but when she realized what he had done to himself, she began to fear what he had done to her and refused to leave. She never spoke again.
For many years, Essex (now calling himself Mister Sinister) traveled the world, constantly pursued by his old friend, James Xavier. During that time, he created the first of his mutates, which included the man who would eventually become known as Jack the Ripper.
Following the births of Scott Summers and Jean Grey many years later, he took great interest in their lives for unknown reasons. During the X-Men's raid on the mutant registration building, in which Morph was left behind, believed dead, Sinister took Morph from the scene. He healed Morph, but also brainwashed him into hating the X-Men.
- Voiced by Christopher Britton
- 16 appearance(s) of Nathaniel Essex (Earth-92131)
- 6 minor appearance(s) of Nathaniel Essex (Earth-92131)
- 4 mention(s) of Nathaniel Essex (Earth-92131)
- 22 image(s) of Nathaniel Essex (Earth-92131)
- 1 quotation(s) by or about Nathaniel Essex (Earth-92131)