Minotaur

The Minotaur was a creature from Greek mythology, said to have the head of a bull and the body of a man.

The Doctor and Zoe encountered the Minotaur in the Land of Fiction. It vanished when they denied its existence. (DW: The Mind Robber)

The Doctor later learned that the myth of the Minotaur was real during a trip to Atlantis. The creature was formerly a member of Dalios's court, a great athlete who desired the strength of a bull and a long life in which to use it. Kronos granted him his wish, and the creature was made guardian of the Kronos Crystal until the Doctor defeated it. (DW: The Time Monster)

The Greek hero Theseus was renowned for fighting the Minotaur. The Doctor claimed to have given Theseus the ball of string he used to find his way around the labyrinth in which the Minotaur resided. (DW: The Creature from the Pit)

It is unknown if this is the same Minotaur from Atlantis or a different one.

Extraterrestrial life forms which resembled Minotaurs include the Nimon and the Tauride. (DW: The Horns of Nimon, DWBIT: Minor Trouble)