Seth Rogen has fulfilled a dream, and he's not talking about starring in the box-office hit "Knocked Up" or playing a superhero in the upcoming "Green Hornet."
Rogen co-wrote an episode of "The Simpsons" and lends his voice to a character in the episode that airs 8 p.m. EDT Sunday, kicking off the Fox show's 21st season. He's only the second visiting celebrity to both write and act, following in the 2006 footsteps of Ricky Gervais.
"As a writer, it always just seemed like the Holy Grail," Rogen said of the animated series. "I can die a happy man now."
The episode, by Rogen and writing partner Evan Goldberg in collaboration with the show's writers, plays off the actor's pre-filming fitness regimen for "Green Hornet." The movie is in production and set for release in 2010.
In "Homer the Whopper," Rogen plays a trainer assigned to get Homer Simpson in superhero shape to play Everyman, a comic book hero created by the rotund couch potato.
"We wanted to comment on how Hollywood generally ruins these movies. The whole joke is Homer is cast to play a guy who's an everyman and they try to make him into this physically fit guy," Rogen said.
Recording with the cast was "one of the highlights of my life," said the seriously devoted "Simpsons" fan (favorite episodes include "Itchy & Scratchy Land" and the one in which Bart sells his soul to Milhouse).
"It was completely surreal. I was just in shock afterward. I felt like I had gone skydiving or survived an earthquake," Rogen said.
Other celebrities to be heard on "The Simpsons" this season include Sarah Silverman, Angela Bassett, Eli Manning and Bob Costas.
As for Rogen's part in "Green Hornet," he's still processing his on-screen switch from lovable schlub to dapper leading man. He and Goldberg wrote the screenplay.
"It's odd to see yourself looking cool when you're someone like me," Rogen said, laughing. "It's just not something I'm used to."