Tarzan Alive: A Definitive Biography of Lord Greystoke is a fictional biography by American author Philip José Farmer that alleges the life of Edgar Rice Burroughs' character Tarzan is the story of a real person.

Farmer examines the psychological make up of John Clayton (Tarzan's real name in the novels) and his peers, based on close readings of the various Burroughs books, accepting some of Burroughs' concepts and rejecting others in an attempt at greater verisimilitude.

Among his conceits is that, since the apes described by Burroughs had a spoken language that Tarzan learned, these animals must have been "pithecanthropoids": "a group of rare hominids who are probably now extinct" and "not great apes".

A more recent reprint of Tarzan Alive includes a new foreword by Win Scott Eckert and introduction by Mike Resnick, along with "An Exclusive Interview with Lord Greystoke" and "Extracts from the Memoirs of "Lord Greystoke".

The text of Tarzan Alive links the characters from the Tarzan mythos to dozens of other fictional literary characters as members of Farmer's "Wold Newton family".