AGE: 21
HOMETOWN: Portland, Ore.
LATEST GIG: Summer's new boyfriend Zach

•Lead on, Macduff.
As a high school junior he was cast as Macduff's son in a community theater production of Macbeth. A local critic panned the show but praised him. Cassidy says, laughing, "All my castmates were ripping me apart! You don't want to be singled out as the only person that's good."

•Cape fear.
After two years at New York's New Actors' Workshop, Cassidy went to Los Angeles in 2004 to try out for the title role in the upcoming Superman Returns. When he put on the suit, "I was absolutely terrified," he says. He didn't get the part but impressed McG, then the film's director and an executive producer of The O.C., who got him an audition as Zach.

•Slipped lips.
Cassidy (who has a girlfriend) was uptight in his first kissing scene with Summer (Rachel Bilson). "I didn't get my face within six inches of hers. Rachel goes, 'Just chill out, you're going to be okay.'"

•So who's geekier?
"I think I'm a close second to Adam Brody [Summer's ex-beau Seth]. Because he actually likes comic books. I've never read one. Oh, but wait! I play golf a lot."