Michael J. Fox outside the Ed Sullivan Theater for the 'Late Show With David Letterman'. New York City, USA - 02.04.09

The actor plays the disabled love interest of Janet Gavin, the ex-wife of lead actor Denis Leary's character Tommy Gavin, in the gritty firefighter series, and Fox embraced the idea he'd be playing an ill-tempered bad guy.

He says, "People don't often think of me as a bitter misanthrope, so to get to play one, it's too fun to pass up."

Source: WENN