Nathaniel Essex(Mr. Sinister)

Nathaniel Essex was born in 19th century England. He became a scientist and eventually married Rebecca Milbury, who bore him a son. When their son dies from birth defects at the age of four, Essex dives into his work, studying genetics and experimenting to find ways around humanity's vulnerabilities. After hiring the Marauders to collect deformed people from the streets on whom he can perform experiments Essex's work catches the interest of En Sabah Nur, and when Essex and Nur visit The Hellfire Club, Nur revealed his powers as Apocalypse, providing the proof of his theories that Essex sought. At this point, Cyclops and Phoenix are sent from the future to prevent the early coming of Apocalypse, but they are instead captured by him. Essex returns home to his wife and an unborn child, set to bury himself once more in his science, but he finds his wife has freed his captives and given birth to his second child early; she is dying from stress. Rebecca's last words to Nathaniel are that he is contemptibly sinister, and so he changes his name to Mr. Sinister and becomes the prelate to Apocalypse. He is granted immortality through a painful transformation involving Celestial technology, which also changes his appearance to the deathly pale skin and red eyes lacking pupils which we are familiar with as his Mr. Sinister persona.