Spader was my first and only choice. He’s got that hypnotic voice that can be eerily calm and compelling, but he’s also very human and humorous. Ultron is not Hal [from 2001: A Space Odyssey]. Spader can play all of the levels. He’s the guy to break The Avengers into pieces.
Joss Whedon on why he cast James Spader as Ultron (X)