Marvel Entertainment has featured an interview with Avengers: Age of Ultron director and screenwriter Joss Whedon, in which he discussed James Spader's experience in bringing Ultron to life. "He has that voice, that very terrifying 'I own everything' maleficent evil voice and then suddenly get very peevish about something, He can go from very intense to very comedic, and get there on a dime beautifully," Whedon said when talking about Spader's voice performance.
In the comic books, Ultron's face isn't animated, but for the film "his face is articulated." Whedon said that Spader had to wear motion-capture gear. "It was a nightmare for poor James because he wears glasses, which he could not wear," Whedon explained. "And he was wearing a helmet with two cameras with light on them shining into his eyes and he has to go around set like he is an eight foot robot quickly and confidently over these jagged sets."
Watch his interview below: