“You use it or you lose it,” she responded to San Diego Magazine in 2007 when asked about that complaint. “If we’re not out there — if we don’t keep up the reminders and remembrances — you fall off. And as long as I’m here, that isn’t going to happen.”

In 1993 she founded Dr. Seuss Enterprises, whose stated mission was to “protect the integrity of the Dr. Seuss books while expanding beyond books into ancillary areas.” That meant keeping a sharp eye on copyrights and trademarks as Dr. Seuss merchandise and spinoffs were sold around the world.

It also meant overseeing several film adaptations of his work, among them computer-animated adaptations of “Horton Hears a Who!” and “The Lorax,” as well as the 2000 live-action film “Dr. Seuss’ How The Grinch Stole Christmas,” starring Jim Carrey, which was one of the worst-reviewed movies of the year and yet one of the highest-grossing. (Ms. Geisel was the executive producer on many of these film projects, most recently the animated “Grinch,” starring the voice of Benedict Cumberbatch; it opened last month to mediocre reviews.)

Not everything made money. The 2000 Broadway show “Seussical” was a flop. And Ms. Geisel did not hide her annoyance that Universal Pictures cast Mike Myers in the title role of “The Cat in the Hat” (2003), which also sagged at the box office. She felt he was ill suited for the part. The reviews were terrible — A. O. Scott of The New York Times called it “a vulgar, uninspired lump of poisoned eye candy” — and it prompted Ms. Geisel to declare that she would never allow another live-action portrayal of Seuss characters.

Over the years she repeatedly told interviewers that she was still recovering from that experience. As she often put it, “I’m just getting my ‘Cat’ out of the litter box.”