Now that Marvel fully owns the right to the X-Men, there's no excuse to keep ignoring one of their best and most often overlooked enemies. From Magneto to Dani Moonstar's Demon Bear, Fox's X-Men movies adapted several X-Men villains in the span of twenty years. Some of them were better received than others, and each of their characterizations varied in accuracy to the source material.

Many of the X-Men's most famous villains never got to appear in any of Fox's live-action Marvel films. Exodus, Onslaught, Destiny, Omega Red, Nimrod, Stryfe, and Madelyne Pryor are only a few of the comic book villains that have yet to make it to the big or small screen in live-action. Fortunately, Disney's acquisition of 20th Century Fox means that Marvel Studios possesses the full cinematic rights to the X-Men, and the MCU's Phase 7 will likely start covering all the areas that Fox's X-Men franchise left unexplored.

Mister Sinister Is The Perfect Villain For The MCU's X-Men

Mister Sinister Represents Everything Mutants Fight Against

Mister Sinister is the first non-mutant character to accurately predict the next step of human evolution, which leads him to develop an obsession with mutants decades before the first mutant goes public. Nathaniel Essex's most twisted clone shaped mutant history for decades before Charles Xavier got the idea to assemble the X-Men, having received a mutant upgrade from Apocalypse himself. As a mutated human clone, Mister Sinister embodies humankind's inevitable aggression towards mutants, as well as the evil potential of mutant villains.

The emergence of mutants is precisely what Nathaniel Essex has been preparing for, so it only makes sense for Mister Sinister to pop up right as the X-Men appear for the first time

Fox's X-Men movies never featured Mister Sinister, but they laid the foundations for more ambitious stories, as they covered the basics of the X-Men's lore. Since general audiences are more than acquainted with mutant lore (and they have fourteen movies to revisit it), the MCU can jump straight into complex villains like Mister Sinister and deeper parts of the X-Men's comic book history right away. To begin, the MCU could reveal how Mister Sinister has been preparing to face mutants for decades in the MCU's main timeline.

Mister Sinister's introduction in Marvel Studios' first X-Men movie would suit the timing of the first chapter in the MCU's mutant history. Regardless of whether Avengers: Secret Wars presents a soft-reboot of the franchise or not, Mister Sinister could unveil himself at the same time as the X-Gene is discovered at the start of Phase 7. After all, the emergence of mutants is precisely what Nathaniel Essex has been preparing for, so it only makes sense for Mister Sinister to pop up right as the X-Men appear for the first time.

Mister Sinister Almost Appeared In Fox's X-Men Movies More Than Once

Fox's X-Men Movies Were Building Up To Mister Sinister's Introduction

Despite his absence, Mister Sinister was extremely close to appearing in an X-Men movie for years. The first major hint at Mister Sinister came in X-Men: Apocalypse's post-credits scene, which revealed that “Essex Corporation” agents collected Wolverine’s blood following his escape from the Weapon X program. Logan scrapped the idea of Mister Sinister's involvement and replaced the Essex Corporation with Transigen and Nathaniel Essex with Xander Rice. Deadpool 2 revealed that Firefist was experimented on in the Essex House for Mutant Rehabilitation and The New Mutants revealed that Dr. Cecilia Reyes was actually working for the Essex Corporation all along.

Mad Men star Jon Hamm once revealed he was in talks to play Mister Sinister in an X-Men movie.

Writer Byron Burton worked on a script for a canceled X-Men movie called X-Men: Fear The Beast, where Mister Sinister would have gotten his hands on a modified version of Hank McCoy's antidote to heal his own wounds. Even then, X-Men: Fear the Beast would have only added yet another set-up to Mister Sinister's proper introduction in an eventual X-Men movie. Looking back, it's evident that plans for Mister Sinister's live-action debut intended him to be a villain on the level of the MCU's Thanos, but also that Fox didn't have a solid idea of what that debut would look like. Now, Marvel Studios can start from scratch without needing to address all of Fox's abandoned set-ups.

It's Actually Great That Mister Sinister's Live-Action Debut Has Taken Too Long To Happen

Mister Sinister Was Too Complex A Villain For Fox's Pre-MCU X-Men Movies

It's a shame that Fox's X-Men characters may never get to cross paths with Mister Sinister on-screen, but on the bright side, it may have been for the better. While Fox's take on the X-Men was extraordinary for its time, many character portrayals suffered because the franchise simplified them and grounded them too much in reality. Fox faced the colossal task of adapting the X-Men to live-action at a moment in time when superheroes had to rely on realism. As a result, some elements had to be tonwed down, like the X-Men's costumes, which had to start off as leather uniforms in order to be welcomed by general audiences who weren't well acquainted with the source material.

The X-Men movies evolved and took bolder risks throughout the years, but characters like Jubilee, Emma Frost, Gambit, Storm, Jean Grey, and Cyclops were stuck on surface-level adaptations. Apocalypse's conquest, for instance, was a far cry from Magneto's relatively grounded plans for mutant liberation, but X-Men: Apocalypse couldn't handle its source material appropriately in the span of a single movie. Despite Oscar Isaac's talent, Apocalypse came across as a stereotypical supervillain, and his costume and make-up didn't capture his comic book counterpart's terrifying appearance. Had Fox introduced Mister Sinister in time, the studio would have risked making the same mistakes.

What Mister Sinister Storylines The MCU Could Adapt

Marvel Studios Has Plenty Of Mister Sinister Material To Adapt

Apart from Nathaniel Essex's origins and discovery of mutantkind, the MCU could explore Mister Sinister's long history of manipulating mutant DNA, including his experiments on Scott Summers a.k.a. Cyclops and Jean Grey, which ties into the creation of Cable and the legacy of the Summers bloodline. Mister Sinister's experimentation with genetics and time travel could allow the MCU to build long-term narrative threads that encom the whole Mutant Saga. Not to mention, his ties to Apocalypse could also give En Sabah Nur another chance to shine in the MCU.

Mister Sinister's on-screen debut would have to arrive soon in order to avoid the same mistake Fox's X-Men movies made with the villain

Additionally, the MCU could adapt elements from Marvel Comics storylines such as Inferno, where Mister Sinister is revealed to have created Madelyne Pryor; Messiah Complex, where Sinister initiates a hunt for Hope Summers; and Kieron Gillen's Uncanny X-Men run, where Mister Sinister creates an entire city full of clones of himself. Otherwise, Marvel Studios could make Mister Sinister a mysterious mastermind that pulls the strings from the background, influencing other villains to do his bidding before facing the X-Men by himself. Of course, Mister Sinister's on-screen debut would have to arrive soon in order to avoid the same mistake Fox's X-Men movies made with the villain.