There is no star on the star dressing room at the Gershwin — just a sign, and it couldn't be clearer: "Nobody Is To See the Wizard, Not Nobody, Not Nohow." Nevertheless, the door opens a crack, and a human eye appears about five feet off the ground, crinkling with fun and mischief. "Not YOU," decrees the bogus bass inside. "YOU can come in."

Not that you'd notice from all the stylish, meticulous strutting he does across the stage, but the sprite in Joel Grey is 71 years old in human years — and it's given full rein in Wicked, the $14 million musical fantasy Stephen Schwartz and Winnie Holzman have made of Gregory Maguire's best-selling "backstory" of The Wicked Witch of the West.

Grey plays a role listed as "The Wonderful Wizard of Oz" — every inch of it — and that's seconded by a show-stopping song and dance called, simply and accurately, "Wonderful." It's not easy to make an understatement of that adjective, but Grey manages to do it.

Mind you, he's the last cog in place, arriving in the second hour of the first act ("I start getting ready as the overture begins — that's my cue"), but the applause he draws is the kind that welcomes a beloved actor to a beloved role. It keeps the kid in him alive and kicking. "I don't get the whole age thing. I mean, Elaine Stritch's out there, Barbara Cook's out there — no one thinks twice. I don't know what age is. I don't think about it."

Like his last Broadway appearance six years ago — Amos Hart, the forgotten man of Chicago (a.k.a. "Mister Cellophane") — the Mister Wonderful of Wicked is a scene-stealer in short doses, but his three scenes earn him top dollar and third billing (after Kristin Chenoweth's Glinda and Idina Menzel's Elphaba). Obviously, it sits well with him: "How often does a guy get to be the only person in the world who can sing, 'I'm off to be the Wizard, the Wonderful Wizard of Oz' — eight times a week? For me, I'm always looking for the truth of the man. I didn't look at the movie when I knew I was going to do this. I wanted to rediscover it on my own. Between Joe Mantello, the director, and Susan Hilferty, who did costumes, we found a world for him." Personally, he has something else that keeps him younger than springtime — a girl named Stella, the baby of his actress-daughter, Jennifer Grey, and her actor-husband, Clark Gregg — and, boy, does he have a lullaby for her! "Wonderful/My Stella's wonderful . . . "

The grandfather from Oz exits, grinning.