The Avengers stars have been dishing out some details on the sequel's villain Ultron.
Comic book fans will already know that the supervillain, to be played by James Spader, was built by scientist Hank Pym (the first Ant-Man), but for The Avengers: Age Of Ultron, he will be the handiwork of Robert Downey Jr's Tony Stark.
"It's not the good version that could've come from [Stark's] intellect and personality. It's the bad son," Chris Hemsworth, who will return to play Thor, told Entertainment Weekly.
Ultron was built as the ultimate drone to help the superheroes protect the world, but turns rogue after Tony uploads his cynicism - but not his sympathy - into the robot.
Chris Evans, who reprises his role as Captain America, admitted Ultron isn't a dumb drone that merely submits to commands.
"A lot of times when Ultron starts talking, it's beautiful. It's really intelligent stuff," the actor said.
"He's out to do the things he wants to do because he's disgusted with X, Y and Z. You could probably sit down with Ultron and have a really intelligent conversation. He could blow your mind with his views," he continued, before adding: "Yeah, and then kill you."
In one of the opening scenes of the next instalment, Ultron and his team of Legionnaires attempt to eradicate humanity and kill the superheroes, which includes Stark, Thor and Captain America, alongside Scarlett Johansson's Black Widow, Jeremy Renner's Hawkeye and former S.H.I.E.L.D. agent Maria Hill (Cobie Smulders).
The Avengers: Age Of Ultron, directed by Joss Whedon, will be released in 2015.