Andrew Rannells Previews His Musical Simpsons Debut — Plus: Watch A Clip

Andrew Rannells is finally stepping into the role he was born to play: Andrew Rannells.

The Girls scene-stealer appears as himself — well, a "boozier, meaner version" of himself, he tells TVLine — on Sunday's episode of The Simpsons (Fox, 8/7c) in which he helps Marge and Lisa repair their fractured relationship.

"They're having some mother/daughter growing pains," Rannells explains. "Lisa finds out Marge has never liked jazz, which is devastating to poor Lisa, so they decide to go on a little weekend trip; they end up seeing a touring production of a musical of Bad News Bears, in which I'm starring as the Walter Matthau part."

Rannells' debut on The Simpsons is a sort of full-circle experience for the Tony Award nominee; the director of his episode, Rich Moore, also helmed one of his personal favorite — and most formative — installments, 1993's "Marge vs. the Monorail."

"I had never seen anything quite like that before," he recalls. "As a kid in Omaha watching that episode, I really felt like I was in on a secret joke. None of the kids I went to school with knew that was [a spoof of] The Music Man, and I felt like my musical theater nerd-ery was all of a sudden paying off. As a kid growing up loving musicals, that episode validated my love of them in a funny way. Here it was on this hugely popular TV show, so I'm doing something right."

In fact, becoming Simpson-ized was such a surreal concept for Rannells, the mere idea of it seemed unfathomable.

"I've been such a fan of the show for so long that it wasn't even on my radar," he says. "It didn't seem within the realm of possibility. I thought my agent was playing some sort of trick on me when I got that phone call."

Fortunately, it wasn't a trick. And even more fortunately, Rannells says, "I'm very happy with the way they did my hair."

Now that you've gotten a taste of what's in store, hit PLAY on our exclusive clip from the episode below: