Paul Rudd has been killing himself every night.

The actor best known for comedies such as "Knocked Up" and "Forgetting Sarah Marshall" has been performing a decidedly darker role on Broadway recently, as a devout man whose loss of faith makes him suicidal in "Grace."

"The guy just plunges off the deep end in a really kind of emotionally raw and draining way," Rudd says during a turnaround trip to Los Angeles to promote his latest film, Judd Apatow's "This Is 40." The actor was back onstage in New York the night after the interview.

He plays against his loveable-good-guy type in both projects. In "Grace," he starts out confident, then unravels. In "This Is 40," he's having a full-on mid-life crisis, dreaming of living a different life while his business struggles and his marriage falters. Rudd stars with Apatow's real-life wife, Leslie Mann, and the couple's two daughters, Maude and Iris, in the comedy in theaters Friday.

Next up is "Anchorman 2," and Rudd says, "I could not be more excited about it." He's ready for a dose of goofy comedy after taking on such a dark stage role, because every character he plays gets under his skin a little.

"It just affects my mood, it affects my outlook in ways that I might not even be aware of," he said.

He recalled his role as an unflappable optimist in 2011's "Our Idiot Brother."

"The character was this guy who just saw the good in everybody and in everything, and I was just in a great mood making that movie," Rudd said. "I just loved playing that part because I kept thinking, I wish I was kind of like this in real life. And it's not like when I finished shooting that day and I go back home I was acting like the character or thinking like the character, but there was something that just kind of seeped in."

Rudd finds he even dresses like his characters when he's not playing them.

"I got kind of hippy-dippy after that movie for a little while," he said. "Or I wore a lot of gingham shirts and V-neck sweaters after 'I Love You Man' ... and I wasn't ready to shave my moustache after 'Anchorman' right away."

The 43-year-old is eager to get into the "Anchorman" sequel, with writer-star Will Ferrell's conceited newsman Ron Burgundy, after the Broadway run of "Grace" ends next month.

"I'd be excited about it anyway" Rudd said. "But it's going to be a nice change of pace from blowing my brains out in this play every night."