Nathaniel Essex, also known as Mr. Sinister, has been a shadow-player in human history for over a century.
Born in 1841, Essex travelled to Oxford University as a young man in 1859. He developed advanced theories on evolution and began intensive study of the concept of genetics. He became obsessed with Darwin and Gregor Mendel, and then turned into chromosomal genetics after the publication of Flemming's work on the subject. He quickly established himself as a leader in the field of genetic theory, inspiring individuals such as Reginald Punnet during his tenure at Oxford. Essex married an Englishwoman named Rebecca shortly after concluding his baccalaureate work. She gave birth to a son in October of 1872. Intellectual curiosity on genetics turned to obsession after the death of Essex' son Adam, who died at just over a year old due to a number of genetic disorders.
In 1872, Essex-- now a respected doctor and medical man-- began pursuing unethical practices in his search for knowledge. Essex began diving into graveyards and culling live test subjects. Inspired by Victor Frankenstein, Essex even exhumed his son's corpse and suspended it in an incubation fluid chamber. Driven apart by his insatiable focus, his wife Rebecca left him several times to live with her family. In his bitter loneliness, Essex met the man who would shape his destiny for the next century: En Sabah Nur.
Nur provided Essex with the bulk of research dating back thousands of years, some of it obscure and arcane-- other portions of it clearly derived from technology far in advanced of Essex' machines. But with Nur aiding him, Essex completed his magnum opus in 1873: "On Mutants," a treatesie correctly identifying the chrosomal markings for Homo Superior. Nur offered the brilliant doctor immortality in exchange for service, a thousand lifetimes to pursue science unfettered by the laws of man. Essex declined.
Shortly after the book was published, Essex discovered his wife Rebecca was pregnant. The timing of the news combined with his success seemed to release him from the ghosts of his past. The doctor resolved to quit his fields of practice and returned home, intent on rejoining his wife and dedicating himself to his family.
To his horror and dismay he realized that Rebecca had penetrated his secret labs and had a severe miscarriage while in the process of freeing his subjects. Her last works to Essex were: "To me, you are... utterly… and contemptibly… sinister!"
Essex accepted Nur's offer in 1874. Using Terrigen Mists stolen from the wreckage of the original Inhuman colony ship, Nur directed Essex into painful forced evolution, kept alive by the arcane technologies of a Celestial science vessel that Nur had commandeered some 800 years prior. Essex emerged from the other end more ghost than human.
He chafed under Nur's influence, and relocated to New York in 1882. There he met the progenitor of the Summers Clan, Daniel Summers, and began a long-term breeding program aimed at encouraging metahumans to reproduce with one another. While living in New York, Sinister was approached by another immortal, one older even than Nur. Vandal Savage recognized the virtue of Sinister's work. Savage and Nur had clashed repeatedly over the aeons. Savage explained that Nur had been corrupted by his Celestial technology. Savage assisted Sinister in developing a modified version of the Techno-Organic Virus and infected Nur with it while the First Mutant was emerging from stasis under London. This defeated Nur's ambition to conquer the world and forced him back into his Celestial sarcophagus for decades to come.
Essex was inducted into the ranks of the Harbingers and became one of the principle actors contributing to the start of World War II. He adopted the name Josef Mengele and resumed his barbaric experiments under the protect of Nazi Germany, attempting to further deconstruct not just mutant chromosomes, but the Celestial DNA encodings that gave people superhuman abilities. His research was interrupted by US Soldiers under the command of Steve Rogers attacking his concentration camps, and Sinister fled to South America to evade capture.
Post-war, Essex adopted a new name-- Nathan Milbury-- and moved to New Mexico. He joined Project: Black Womb, a genetic research program aided with some of the finest contemporary minds in the field. He became a chief contributor to both CADMUS and their mission of metagenetic research, and Weapon Plus as they attempted to develop this research into practical applications. Major breakthroughs occurred in the '60s and '70s, notably when CADMUS deciphered the genetic code of Logan Howlett and began successfully retro-engineering his DNA into donors. The shadow program Weapon X was developed simultaneously, and when it was shut down Essex disappeared from view once more. 'Nathan Essex' once more, he established an orphanage called the State Home for Foundlings in Nebraska which operated from 1980-2000. In this orphanage, Essex spent a substantial amount of time manipulating children psychologically and experimenting on them in an attempt to produce a metagenetic episode. He also discovered Scott Summers, who would become a personal nemesis and a source of endless curiousity due to unique characteristics of his genetic code.
In 2011, Charles Xavier and several of his allies/students liberated the children from the Home for Foundlings. Scott Summers led the charge, and Sinister was once more forced to flee and abandon his research. Kidnapped children were returned home, and several orphans were adopted by the Xavier Institute.
Sinister resurfaced in 2020.