Wikipedia: Minotaur

In Greek mythology, the Minotaur was a creature that was half man and half bull?, that was also known as Asterius or Asterion, a name shared with Minos's foster father. "Minotaur" is simply Greek for "Bull of Minos." It dwelt in the labyrinth, which was an elaborate maze constructed by King Minos and designed by Daedalus to hold the Minotaur.

Poseidon promised King Minos to offer him a bull on condition he would sacrifice the bull back to the god. Indeed a bull of unmatched beauty came out of the sea. King Minos seeing it, did not want any more to sacrifice it. He instead sacrificed another bull, hoping that Poseidon would not notice. Poseidon was very angry when he realised what had been done so he caused Minos's wife Pasiphae to be overcome with a fit of madness in which she fell in love with the bull. Pasiphae went to Daedalus for assistance, and Daedalus devised a way for her to satisfy her passions. He constructed a hollow wooden cow covered with cowhide for Pasiphae to hide in and allow the bull to mount her. The result of this union was the Minotaur. In some accounts, this bull went on to become the Cretan Bull captured by Heracles for one of his labours.

Every year the Minotaur was fed the seven young men and girls sent to Crete as the tribute from Athens. The beast was finally slain when Theseus offered himself as part of the tribute and with the help of Ariadne?, Minos's daughter, entered the labyrinth and not only defeated the creature but managed to escape having tied a piece of string to the entrance so that he could follow his way back through the labyrinth to the exit.