During her lifetime, Catherine made many enemies throughout Europe. After her death, the horse myth probably emerged from the French upper class as a way to mar her legend. "She was a woman in power with a promiscuous sex life," says Michael Farquhar, author of A Treasury of Royal Scandals. "Her contemporaries were never comfortable with that."

From France, the myth may have traveled into the American press, which was famous for printing scandals at the time. "The press of our Founding Fathers makes the National Enquirer look tame," says Farquhar.

The salaciousness of a rumor often helps it survive. People repeat shocking stories if only to see whether they can be confirmed, and the very act of repetition adds credibility to the story. Since bestiality has remained socially unacceptable, the myth about the ruler and her horse never lost its power to outrage.

Many rumors survive on shock value combined with a nugget of truth. Catherine the Great did not look for fulfillment in the royal stables, but she did handpick lovers from the royal cavalry. Hitler was not impotent, though he had only one testicle. Caligula did not eat his sister's fetus, though he committed incest with at least one of his sisters, possibly all three.

J. Edgar Hoover was not a cross-dresser, but he did carry on a 40-year love affair with his right-hand man, Clyde Tolson. Peter Pan author James Barrie was not a pedophile, though he loved to play with little boys. And Michael Jackson? Well, you decide.