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Count Loudon Wainwright III as one of Judd Apatow‘s merry band of repertory players.

The singer-songwriter, best known for ’70s novelty hit “Dead Skunk” and son Rufus, appears in “Knocked Up” as Katherine Heigl‘s OB-GYN. He co-wrote the pic’s soundtrack with Joe Henry.

This follows earlier appearances in Apatow’s first film, “The 40-Year-Old Virgin,” and Fox skein “Undeclared.” Wainwright has popped up onscreen intermittently throughout his musical career, playing a singing surgeon on “MASH,” and in parts on “Grounded for Life” and “Ally McBeal,” plus “Big Fish,” Elizabethtown” and “For Your Consideration” for the bigscreen.

Apatow first discovered Wainwright when he was David Letterman‘s sidekick on his morning show. He recruited him to compose the “Knocked Up” score after hearing him perform “Grey in L.A.,” the song that kicks off “Strange Weirdos,” an album of song inspired by the film.

Apatow considers the singer a touchstone for his work, writing in the album’s liner notes: “If I had never been exposed to Loudon, I would probably just be writing fantastic dick jokes, but nothing more.”

“It’s quite a responsibility,” jokes Wainwright, who says he’s glad to be one of Apatow’s merry pranksters along with the likes of Seth Rogen and Steve Carell. “I may be the oldest one, but hanging out with them makes me feel young.”