For what it’s worth — and we’re talking millions of dollars here — you are never going to see as convincing an impersonation of a two-dimensional cartoon by a three-dimensional human as that provided by Ethan Slater at the Palace Theater. Mr. Slater plays the title role in “SpongeBob SquarePants: The Broadway Musical,” the ginormous giggle of a show that opened on Monday night.

This may sound like dubious praise. But think about it. How many of those legions of figures who gambol through stage adaptations of animated movies — teapots, lions, fake Russian princesses, ad infinitum — seem to have been transliterated from the screen without any dilution of their inked-in essence?

The 24-year-old Mr. Slater, making his Broadway debut in Tina Landau’s exhaustingly imaginative production, achieves this metamorphosis sans prosthetics, skin dye or a facsimile costume. (He wears suspendered plaid trousers, with a shirt and tie.) And he’s playing a sea creature from a television children’s show, for God’s sake, one that appears to be a bright yellow, rectangular kitchen sponge.

But though he is neither square-shaped nor visibly jaundiced, I, for one, never doubted that Mr. Slater is SpongeBob to the tips of whatever the underwater phyla equivalents of fingers are. Try that on for size, Mr. Christian Bale, and all you other body-morphing Method boys.