An American author of science fiction, crime fiction, and fantasy, he won a Hugo Award and three World Fantasy Awards. He is known for his Vergil Magus series, as well as for such stand-alone titles as Masters of the Maze (1965) and Clash of Star-Kings (1966).
He served as a medic with the Marine Corps in the Pacific theater of World War II.
He had a reputation for being both short-tempered and generous.
He grew up in New York and later moved to Washington. He and his wife, Grania Davis, had one son together.
He won the Hugo Award, an honor named after writer Victor Hugo.