Mister Sinister as drawn by Ron Frenz.
|First appearance||Uncanny X-Men #221 (Sept. 1987)|
|Created by||Chris Claremont
|Alter ego||Nathaniel Essex|
|Notable aliases||Nathan Milbury, Robert Windsor|
durability and longevity
Mister Sinister is a fictional character that appears in comic books published by Marvel Comics. The character first appeared in Uncanny X-Men #221 (Sept. 1987) and was created by writer Chris Claremont and artist Marc Silvestri.
Debuting in the Modern Age of comic books, the character has appeared in a number of X-Men titles including spin-offs and several limited series. The character has also featured in associated Marvel merchandise including animated television series; toys; trading cards and video games.
Writer Chris Claremont conceived Mister Sinister as a new villain for the X-Men, having felt "tired of just going back to Magneto and the Brotherhood of Evil Mutants and the same old same old" Claremont recalled:
"Dave Cockrum and I were over ideas and what we were coming towards was a mysterious young boy - apparently an 11-year-old - at the orphanage where Scott (Cyclops) was raised, who turned out to be the secret master of the place. In effect what we were setting up was a guy who was aging over a lifespan of roughly a thousand years. Even though he looked like an 11-year-old, he'd actually been alive since the mid-century at this point - he was actually about 50 [...] He had all the grown up urges. He's growing up in his mind but his body isn't capable of handling it, which makes him quite cranky. And, of course, looking like an 11-year-old, who'd take him seriously in the criminal community? [...] So he built himself an agent in a sense, which was Mr. Sinister, that was, in effect, the rationale behind Sinister's rather - for want of a better word - childish or kid-like appearance. The costume... the look... the face... it's what would scare a child. Even when he was designed, he wasn't what you'd expect in a guy like that." 
Mister Sinister debuted in the title Uncanny X-Men, briefly mentioned by Sabretooth during the Mutant Massacre crossover as the leader of the Marauders who had sent them to slaughter the Morlock population.  In the following issue, the X-Men member Psylocke picks up a shadowy mental image of the Marauders' "Master" from Sabretooth's mind.  Mister Sinister finally appeared on-panel in issue #221 (Sept. 1987). The character plays a major role in the Inferno crossover,  where it is revealed that Sinister cloned Madelyne Pryor from Jean Grey for the purpose of her to mate with Cyclops and produce a child, their son Nathan;  Sinister also reveals to have manipulated Cyclops' life since early childhood. After a battle with the X-Men and X-Factor, the villain is apparently destroyed by Cyclops' optic beam. 
Classic X-Men #41 - 42 (Dec. 1989) details the role Mister Sinister played in Cyclops' life at the orphanage in Nebraska. The story features a boy named Nathan who is obsessively fixated on Cyclops - and whom Claremont intended to actually be Mister Sinister. However as Claremont left the X-Men comics, this origin was never picked up. 
Mister Sinister returns in the title X-Factor, leading the Nasty Boys  and has allied himself with the mutant terrorist Stryfe.  In the crossover X-Cutioner's Song, Sthe character impersonates Apocalypse and uses his Four Horsemen to capture Cyclops and Jean Grey.  Sinister hands them over to Stryfe in exchange for a canister containing his genetic material,  but finds it empty.  Afterwards, Sinister confronts Cyclops to reveal that the canister contained the deadly Legacy Virus. 
In 1996, Mister Sinister's origin story was told in the limited series, The Further Adventures of Cyclops and Phoenix. It establish the character as Nathaniel Essex, a scientist from the 19th century obsessed with evolution who made a pact with the ancient mutant Apocalypse to become a virtually immortal being.  It is furthermore established that Mister Sinister created Cyclops' son Nathan - who became the time-traveling soldier Cable - to destroy Apocalypse. 
Mister Sinister appears in the title Gambit  and a connection between the character and the X-Men member Gambit is revealed. The character also attempts to use the High Evolutionary's space station to mutate the human population but is stopped by the X-Men.  The character as well appears in the alternate universe title Mutant X.   In the comic book series Weapon X, Mister Sinister experiments on mutants under the guise of Dr. Robert Windsor and it is revealed that the character worked alongside the Nazis during World War II. The character also appears in the non-canon miniseries, X-Men: The End and the limited series X-Men: Colossus - Bloodline.
Mister Sinister reappears in X-Men: Endangered Species crossover, sending the Marauders and Acolytes out to murder all those who have knowledge of the future;  In the Messiah Complex crossover, Sinister seeks out the first mutant child born since Decimation. However, the character is killed by Mystique who presses his face onto an unconscious Rogue. 
The title X-Men: Legacy reveals that Mister Sinister has implanted his own DNA into certain individuals, including Professor Charles Xavier, and upon Sinister's death, a machine will trigger the imprints, and the individual will be transformed into a new Mister Sinister.  Sinister manages to take control of Professor Xavier's body to save him from a gunshot wound,  however, the combined efforts of Sebastian Shaw and Gambit destroys the machine, enabling Xavier to successfully drive Sinister's consciousness from his mind and body. At the end, a female character appears called "Miss Sinister".  Her real name is Claudine Renko, and possesses telepathy and a healing factor similar to Sinister, but not the memories or mind. 
Mister Sinister is a genetically altered human with superhuman physical and mental abilities. The character is telepathic, able to manipulate the minds of others in various ways, and is capable of energy projection through telekinesis.  Using genetic material from the mutant Courier, Mister Sinister gained complete control of his body at the cellular level, allowing him to shape-shift;  regenerate  and be virtually immune to injuries.   The character has exhibited the ability to teleport, though Beast believes this is accomplished through his tesseract headquarter. 
Mister Sinister is also a scientific genius, with expertise in the fields of biology; genetic manipulation; cloning; including physics and engineering. The character is a master manipulator and planner, with decades of genetic research behind him.
In the Ultimate X-Men series, Sinister is reimagined as a heavily tattooed street thug nicknamed after his tattoo. He is a former scientist who experimented on himself and appears schizophrenic, hallucinating of a "Lord Apocalypse" who orders him to kill a number of mutants to complete his transformation.  After commiting suicide,  Sinister returns to life, completes his mission and transforms into Apocalypse.  However, the Phoenix Force appears, destroys Apocalypse's body, revealing Sinister inside. 
The character features in the alternative universe title What If? issues #46 - 47 (Feb. – Mar. 1993); #74 (June 1995) and #100 (Sept. 1997).