The original Minotaur, also known as Asterion, was a vicious creature that was kept as a prisoner by King Minos of Crete (Minotaur literally means "bull of Minos"). Minos had his architect Daedalus, and his son Icarus, create a maze, or labyrinth, to house the Minotaur.
After Minos's son was killed by Athenians, the king demanded that young men and women from Athens be sent as sacrifices to be devoured by the Minotaur. An Athenian named Theseus volunteered as a sacrifice, with the intent of slaying the beast. Minos's daughter Ariadne fell in love with Theseus, and gave him a ball of string so he would not lose his way in the labyrinth. Theseus used the sword of his father, King Aegeus, to kill the Minotaur.
Since then, the term "minotaur" has been used to describe any creature with the features of both bull and man.