Mister Sinister's History
Sinister was once a bioengineer working for Norman Osborn who specialized in urban stealth and mind-altering drugs to create a super-soldier who could evade any form of detection and hypnotically persuade others. After his superiors refused to allow him to test his research on human subjects, he experimented on himself and acquired superhuman powers, but also lost his sanity to schizophrenia in the process, and began to hallucinate a Lord Apocalypse who preached he would usher in a "Final Age" of mutant dominance or the end of the world. For his madness, Sinister was fired from Oscorp. He might have experimented on Gambit during the mutant's youth.
Relocating to New York and dubbing himself Sinister to follow Apocalypse's orders to kill ten "innocent" mutants, Sinister went on a killing spree and murdered several young mutants (possibly Marrow, Maggott, Synch and Destiny), but he failed to kill Jean-Paul Beaubier. He tried to kill the X-Men, but was incapacitated by Rogue and imprisoned in the Triskelion of the Ultimates. It is there that he sees visions of Lord Apocalypse. Ironically, the vision commanded him to choke himself, and he complied.
Sinister survived his suicide attempt and was placed on suicide watch. Despite being on suicide watch, Essex managed to fake his own death and escape from the Triskelion, to complete his mutant murders. Upon killing a certain number of mutants, he transformed into Apocalypse, but was defeated by Phoenix, revealing his human body within the body of Apocalypse.
Roxxon Brain Trust
In the wake of Ultimatum, Dr Essex apparently reformed enough to be hired by the Roxxon corporation for a think tank. He now wears a long-sleeved shirt, to hide his tattoos, and is habitually clean-shaven. After the destruction of Roxxon Corporation, Nathaniel and other members of the brain trust were witnesses of the "bio-incident". They noticed the presence of Spider-Woman at the time of the attack and the emergence of Jessica Drew, who under the name Julia Carpenter entered Roxxon after the attack. After that, Nathaniel with the participants of the Brain Trust, of the investigation in Roxxon, where the latter are grouped Julie Carpenter, but because of the attack on the Baxter Building, isolated in a safe place, where all know, Jessica.
Together with colleagues Nathaniel explains to Jessica everything that they know about Roxxon, trying to earn her trust and get to know her personality, but she spotted the ruse and bound them in webbing and ran away. But with the help of Dr. Sterns with the power of the Hulk, Nathaniel with colleagues managed to get rid of the web, and Sterns caught Spider-Woman.
Later, in a Roxxon laboratory , Essex and participants of the Brain Trust tried to experiment on Jessica. Jessica woke up, and Otto Octavius was revealed to be the leader of the Trust. He tells those present of his connection with Jessica that he was her creator. Then Spider-Man entered and saved Jessica. When both run away from Roxxon, an alien creature attacked the building, apparently killing the entire Brain trust except Otto Octavius.
X-Men
It is later revealed at least Nathaniel Essex and Layla Miller survived the attack. Nathaniel gets to the mental hospital and kills all the staff and patients, then visits Alex Summers in the white room in the company of the Ghost of a Scott Summers. Nathaniel takes Alex himself, and holds it in headquarters Roxxon, to Layla Miller. Layla agreed that Alex knew who this "fourth mutants", and reminded Nathaniel, that they need to find two more mutants, Essex claims that they have entered into a contract with Rasputin. Returning home, Sinister kneels down in front of the mannequin of Apocalypse.
The Final Incursion
Essex most likely died when Earth-1610 came to an end as a consequence of a phenomenon known as the incursion.[8] However, he was later seen zombified in the Deadlands, where he was killed.
