Mark Ruffalo believes in the ''decency in people'' after his wallet was returned to him.

The 46-year-old actor - who stars in new feel-good film, 'Begin Again' - left his wallet in a cab in Chicago but it was returned thanks to the power of social media when a stranger contacted the star to reunite him with his lost item on Twitter.

They tweeted: ''I have your wallet. Found it in a cab in Chicago on Friday. Let me know the best way to get it back to you. Thanks.''

The actor took a few days to see the message but he was quick to tweet back his thanks when he found out.

He said: ''Thank you! Wow! Another point for the decency in people.''

Mark - who also stars as The Hulk in 'The Avengers' movies - reportedly exchanged a few direct messages with the person through the social networking website to arrange the wallet's return.

The actor later said of the good Samaritan: ''You are a hero!''

Meanwhile, Mark recently admitted he would be interested in appearing in a movie about the Hulk.

He said: ''It could get very boring to watch the guy who's moping around who doesn't want to do the very thing that we're all dying to see him do.

''And so I think that's the tough part of cracking that nut. I think that's what's made it problematical in the past. But I do feel like we've gained some ground on this new version of him, which has - he's sort of turning to face himself, and I think the relationship between [Bruce] Banner and The Hulk as a conscious conflict, it could be really interesting.''