At the New York Times:
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.