Bigfoot

Bigfoot was a creature famous for being caught on the Patterson-Gimlin Bigfoot film. Her real name was Geraldine and she told River Song she was upset that she was filmed on a bad hair day. (PROSE: Suspicious Minds)

An episode of The World's Strangest Mysteries covered a Bigfoot sighting. Jenni Marcel later remarked that it was "obviously a man in a gorilla suit". (AUDIO: Kronos Vad's History of Earth Vol. 36,379)

Upon learning that the Doctor was the Merlin of Arthurian legend, Donna Noble began to wonder if he was also secretly Bigfoot, amoung other legendary characters. (PROSE: Legends of Camelot)