Mythology was a form of story-telling used by many races in the universe.
The Doctor had a keen knowledge of mythology which he justified by its relation to fact. According to the Twelfth Doctor, "from time to time, it turns out to be true". (TV: Mummy on the Orient Express)
Greek mythology contained hidden predictions of the future, specifically about the existence of the Minyan race and the Minotaurs. For example, Jason in his search for the Golden Fleece represented Jackson in his search for P7E. (TV: Underworld, The Creature from the Pit)
A British legend arose about the return of King Arthur through his servant Merlin. This turned out to be a prophecy of events which took place in the 1990s in a struggle between the Seventh Doctor and Morgaine. (TV: Battlefield)
Professor Moorhouse was a professor of alien mythology. He once said that the myth of the Foretold went: "The number of evil twice over, they that bear the Foretold's stare have sixty-six seconds to live." According to the Twelfth Doctor, there was a riddle or a secret word that could make it stop, and that some people tried to bargain with it to spare their lives before it killed them to no avail. When the Doctor met the Foretold, he realised that the right phrase was "We surrender," as the Foretold was a soldier in a long-since finished war. (TV: Mummy on the Orient Express)