Long before the Marvel Cinematic Universe’s second Avengers-level threat was named-dropped in WandaVision, there had been speculation that Ultron could make an unexpected return to the franchise after James Spader was spotted among the credited cast members on the show’s IMDb page.
Of course, being listed on IMDb is by no means a guarantee that somebody is going to show up in the project in question, and as the next several episodes progressed, it looked as though the Ultron reference was there solely to begin building towards the reintroduction of Wanda’s brother Pietro Maximoff, who was initially murdered by the genocidal robot but returned in the much different form of Evan Peters from Fox’s X-Men franchise.
However, a new theory has put forward the idea that Ultron has actually been hiding in plain sight all along, although it’s admittedly drawn from a storyline seen in the Avengers Assemble animated series. Still, it does make some sort of sense when you connect the dots, as you can see below.
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While there’s been no indication that Ultron possesses such shapeshifting abilities, WandaVision has hardly been playing by the established rules and regulations of the MCU so far. Not only that, but we technically didn’t see the villain meet his demise at the end of the first Avengers sequel, although the implication was very much that he’d been destroyed by Vision.
WandaVision has already confirmed that acting S.W.O.R.D. director Tyler Hayward wants to get his hands on Paul Bettany’s character’s body without revealing his plans to those working the WestView case, so theoretically, Ultron could have survived and is now intent on discovering how his intended synthezoid vessel has thrived without having to rely on the Mind Stone for power.