Ultron was seemingly a one-and-done villain for the live-action Marvel Cinematic Universe, but he made his presence felt in a big way during the final two episodes of What If...? "Infinity Ultron" conquered his reality and then set his sights on the rest of the Multiverse, leaving The Watcher with no other choice than to assemble the Guardians of the Multiverse.
However, James Spader didn't return to voice the villain and Paul Bettany's talents weren't made use of, despite the fact that he appeared elsewhere in the show and Ultron was in The Vision's body. Ross Marquand, who played Red Skull in the last two Avengers movies, did a great job, and director Bryan Andrews and Head Writer A.C. Bradley have now explained his casting.
"We wanted Ultron to be as terrifying as possible, because he's terrifying, and Paul Bettany is the loveliest man on earth," Bradley explains. "He is such a sweetheart. We felt that, if Paul Bettany using Vision's voice voiced Ultron, it would be too much of a disconnect, because we're asking the audience to believe that this is Ultron in Vision's body and not Vision."
"So by having Ross step in and give an incredibly chilling performance helped us make that clear to the audience, especially people who aren't as familiar with Age of Ultron, Vision, and that whole canon as we are," she concluded.
Andrews adds to that, saying: "It just seemed to make sense. Because in Age of Ultron, they get some version of Jarvis A.I. into Vision so it makes sense that it's that A.I. with that voice that comes out of that body. But the body can be whatever voice it wants because it's this amazing thing of tech. So if a pure Ultron A.I. gets in there, there's no reason why it would sound like Jarvis. It's Ultron injecting himself into this shell, so it's his personality. He could probably choose to sound any way he wants."
"What's interesting is it makes for a brand new type of disconnect where people are seeing Vision's face and they want to hear that voice that they love so much, but they get this evil voice coming out. It's an extra layer of unsettledness and tension."
As for why Spader didn't reprise the role, both Andrews and Bradley said they're under the impression that everyone was contacted to potentially return as their respective MCU characters. With that in mind, it was probably a scheduling issue or lack of interest from the actor when he was approached for What If...? (Dave Bautista, however, maintains that he was never actually contacted).
What did you guys think of Marquand as Infinity Ultron?