Who defeated Wonder Woman?

Giganta

Wonder Woman was defeated by the redheaded giantess known as Giganta.

Doris Zuel was a doctor suffering from an incurable disease and attempted to transfer her mind into Wonder Woman's body. She was thwarted by Wonder Girl but eventually transferred her mind into a comatose circus strongwoman who conveniently had the power to grow to several hundred feet tall.

Doris would thenceforth be known as the supervillain, Giganta.