News broke out about Paul Bettany,aka the voice of JARVIS, has been cast to play Vision in the upcoming movie Avengers: Age of Ultron. As ew.com points out, how can Bettany play Vision if he voices JARVIS? EW suggests that Ultron corrupts JARVIS and makes him turn on Iron Man. There might be truth to this statement.
As shown at ComicCon, a teaser by Joss Whedon showed Iron Man's helmet being transformed into the face of Ultron. Ultron could be a creation of either Tony Stark himself, SHIELD, or some other bad guy. After he is created, Ultron takes control of JARVIS and programs him into becoming a sentient being capable of many things, including hate. So it is then that he turns on his former master, as stated by EW.
Just a theory, but what do you guys think?