The 42-year-old actor, best known for dramas such as Shutter Island and Collateral, will be the third actor to take on Bruce Banner, and his very green alter-ego, in seven years. Eric Bana starred in 2003's Hulk and Edward Norton headlined The Incredible Hulk in 2008.
"It's like Hamlet or Romeo and Juliet, a new actor gets a crack at it every year," Ruffalo told The Los Angeles Times. "But really it's all heady stuff. It's exciting to be here. It's great to be a part of all this."
Also Saturday, Hurt Locker Oscar nominee Jeremy Renner stepped out on stage to publicly announce he'll play super-archer Hawkeye. Renner and Ruffalo were joined onstage by Chris Evans (Captain America), Chris Hemsworth (Thor), Scarlett Johansson (Black Widow), Clark Gregg (Agent Coulson) and director Joss Whedon. The panel was announced by Iron Man 2 co-stars Robert Downey Jr. and Samuel L. Jackson.
"I have had a dream all my life and it was not this good," Whedon said during the panel, according to Cinematical. "This is The Avengers; a team is more than the sum of its parts -- this cast is more than I could have ever hoped for ... and I am going to blow it. I need your love; I need your support."
The Avengers is tentatively set to hit theaters in 2012.