Fans were left stunned when Marvel Studios bosses announced last month (Jun10) that Norton, who played Dr. Bruce Banner and his monstrous alter-ego in 2008's The Incredible Hulk, would not star in the upcoming superhero movie.
A statement declared he would be replaced by an actor who "embodies the creativity and collaborative spirit of our other talented cast members".
Ruffalo was confirmed as the new Hulk as the The Avengers line-up appeared at the Comic-Con event last week (24Jul10) - but he admits he regrets the way the situation unfolded.
He tells EW.com, "I'm a friend of Ed's, and yeah, that wasn't a great way for all that to go down. But the way I see it is that Ed has bequeathed this part to me. I look at it as my generation's Hamlet."
And the actor admits he was petrified before taking the stage at the comic book convention with his castmates, including Samuel L. Jackson, Robert Downey, Jr. and Chris Evans.
He adds, "I was very, very nervous. I didn't know what to expect. That's as close you're going to get to being a rock star as an actor. The fans - they have very strong feelings toward their comic book heroes.
"It was very exciting - and I realised I had some pretty big shoes to fill. Those were my heroes up there! I was a comic book fan growing up. I loved The Hulk and The Avengers - it's just strange to be entering that world as an actor. I never would have imagined that before."
Ruffalo's appointment makes him the third actor to play The Hulk in recent years - Eric Bana took on the role before Norton in Ang Lee's 2003 film Hulk.