There’s a joke that sums up the classic rise and fall of a star, and it goes like this. Director: “Who is Joe Blow?…Get me Joe Blow…Who can afford Joe Blow?…Get me a Joe Blow type…Who is Joe Blow?”

Sutton Foster, opening this week as Princess Fiona in Shrek at the 5th Avenue, doesn’t just know the joke, she’s in the middle of it. “I was at an audition not too long ago and looking at the breakdown [in which directors list the character types they’re looking for], and I saw they had listed ‘a Sutton Foster type.’ And I was like, ‘I’m right here!'”

The desire for a Foster “type” is no surprise, really, because if she were any more likable she might explode. Picture a young and ganglier Mary Tyler Moore, with a big Broadway voice, nonstop energy, and a huge toothy grin. She plays down her dancing abilities (“Triple threat? I would say I’m more of a 2.7”), but her long and limber dancer’s legs are a major part of her appeal, partly because it’s so delightfully unlikely that she’s as sexy as she is. Her greatest asset is a comic talent often compared to Carol Burnett’s, who she says is a personal idol. In a bravura turn in the unexpected 2006 Broadway hit The Drowsy Chaperone, for example, she performed the song “Show Off” while changing costumes onstage, playing water glasses, escaping from a straitjacket, and doing several cartwheels, all while protesting that life in the limelight was behind her.

The pipes came early (“I had a big voice that I was tormenting my family with when I was about 10”), as did a couple of near-misses on Star Search and a failed audition for The Mickey Mouse Club. Before she was out of high school, she’d joined her first national musical tour (The Will Rogers Follies, directed by Tommy Tune), and followed this with several small roles in such Broadway revivals as Grease and Les Misérables. Then in 2002 came her own bona fide Broadway moment, when she was plucked from the chorus of the newly-revised, Broadway-bound musical Thoroughly Modern Millie to take the title role after the lead was fired. The producer’s risk paid off big—the show and Foster both won Tonys. She originated the role of blonde bombshell Inga when Young Frankenstein opened here at the Paramount last year—which then became her eighth Broadway show. Shrek is slated to be her ninth.

Foster’s had a charmed career—though not without plenty of hard work. (She exudes a healthy athleticism that speaks of morning runs and herbal teas.) And it’s been one almost exclusively in musical theater. “Pursuing TV and film is not part of my drive,” she says. “Never has been. I love the energy of the audience.” One small TV role, however—that of Coco, the commonsensical girlfriend of Brett in three episodes of the HBO series Flight of the Conchords—proved unexpectedly popular. “That was just the perfect project,” she says. “I loved their comedy, and there was the music, and it was shot in New York where I live. Now it’s got a cult following. I’m recognized more often for Coco on the street than I am for my theater work.”

She admits that Young Frankenstein ended up being a tougher experience than she expected, particularly after mixed reviews and a lot of negative publicity for high ticket prices. “New York audiences really met us with arms folded,” she says. “It was hard.” She pauses, then mock-collapses on the table. “No, it was terrible.” But her enthusiasm seems entirely unfeigned for Shrek, which she compares to the much-loved Chaperone—a fond recreation of a brainless 1920s musical revue put together by maverick producers Paul Mack and Roy Miller—even though the money behind this one is from corporate behemoth DreamWorks.

“From the inside it doesn’t feel corporate or big,” she says. “It feels intimate and fun. What excited me about it originally was the artists involved, like [Pulitzer-winning playwright] David Lindsay-Abaire and [Tony-winning composer of Millie] Jeanine Tesori,” and despite featuring a green ogre and a fiery pink dragon, the lyrics and story have grown-up appeal, she says.

“It reminds me of Ratatouille, something that a 7-year-old would enjoy but won’t lose the parents. As much as I enjoy doing it, I really love watching it. During rehearsals I’ll sneak off the stage and watch it from the house. I honestly can’t wait to unveil this show.” There’s that big grin again, and what the hell, I’m sold. Her enthusiasm for what she’s doing is of star-like magnitude. I would guess it’ll be quite a while before anyone asks “Who’s Sutton Foster?”