Seth Rogen has co-written the 21st season premiere of The Simpsons.

Rogen lends his voice and writing talent to a character in the airing this Sunday, kicking off the 21st season of the animated classic. He’s only the second visiting celebrity to both write and act on an episode of The Simpsons, joining comic Ricky Gervais, who did the same thing in 2006.

The Green Hornet star calls working with the cast “one of the highlights of my life,” telling The Huffington Post:

“As a writer, it always just seemed like the Holy Grail. I can die a happy man now. It was completely surreal. I was just in shock afterward. I felt like I had gone skydiving or survived an earthquake.”

The season opener, entitled “Homer The Whooper,” was inspired by Seth’s grueling fitness regimen during filming for Green Hornet, set for release in 2010.

Seth plays a trainer assigned to get Homer Simpson shape to play superhero Everyman, a comic book hero he created.

“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,” Seth explains.

A die-hard fan of The Simpsons, Seth’s favorite episodes include “Itchy & Scratchy Land” and” the one in which Bart sells his soul to Milhouse.”