The Cat wore a hat. Everyone knows that.

But so did Sam-I am, the mooing Mr. Brown and the fat fish from “One Fish, Two Fish” — a tiny yellow hat.

The Grinch disguised himself in a crinkled Santa hat.

All over Dr. Seuss’s beloved children’s books, his characters sport distinctive, colorful headwear — unless they are the kinds of creatures that have it sprouting naturally from their heads in tufted, multitiered and majestically flowing formations.

Image This hat from Theodor Geisel's collection resembles the one worn by the Cat in the Hat. Credit... Dr. Seuss Enterprises L.P.

So it’s no surprise that the real Dr. Seuss, Theodor Seuss Geisel, was a hat lover himself. He collected hundreds of them, plumed, beribboned and spiked, and kept them in a closet hidden behind a bookcase in his home in the La Jolla section of San Diego. He incorporated them into his personal paintings, his advertising work and his books. He even insisted that guests to his home don the most elaborate ones he could find.