When Mark Ruffalo won his role as the Incredible Hulk for this month's mega-blockbuster Avengers Assemble, he made one fatal mistake: trawling the internet for reactions. Comic-book fans – particularly those obsessed with the Marvel superhero universe – can be an unforgiving bunch. "It was pretty brutal," he laughs. "It definitely hurt my feelings and scared me." How could it not? Insults ranged from "Ruffalo is a tool" to "That guy is barely awake. How is he going to be pissed off as the Hulk?"
The Wisconsin-born Ruffalo has a sleepy timbre to his voice that would suggest he has no right to play the green-skinned monster with serious anger-management issues. He doesn't do blockbusters – the closest was John Woo's Second World War drama Windtalkers. And his best work has come in the indie world – from his breakthrough as the drifter brother in Kenneth Lonergan's You Can Count on Me (2000) to his Oscar-nominated turn as the roguish sperm donor in The Kids Are All Right.
It didn't help that, unlike his Avengers co-stars – Robert Downey Jnr as Iron Man, Chris Evans as Captain America and Chris Hemsworth as Thor – Ruffalo had not had a previous solo outing to ease his way into this Marvel mash-up, as the superheroes team up against Tom Hiddleston's nefarious Loki. "I definitely felt out of place," he says. What's more, he was entering the franchise as the inheritor of a poisoned chalice – a highly popular character (from both the comics and the television series, starring Bill Bixby) that has twice failed in previous film adaptations.
Unlike Eric Bana (in 2003's Hulk) and Edward Norton (2008's The Incredible Hulk), who were solid as the creature's alter-ego, scientist Bruce Banner, Ruffalo gets to play the creature as well as Banner, thanks to the motion-capture technology that also saw Andy Serkis play Gollum in The Lord of the Rings.
While it meant he was forced to wear unflattering pyjamas for the "mo-cap" process – much to the hilarity of the rest of the cast, who were all dressed in their superhero garb – Ruffalo's features have been brilliantly integrated into the face of the Hulk by FX experts ILM. "Marvel as a rule never wanted the Hulk to look like the actor that was playing Banner. I really pushed hard to make the Hulk look like me."
'Avengers Assemble' is out now