A Minotaur is a creature from Greek mythology that is half human and half bull. It was said to have lived at the center of a great labyrinth (an elaborate maze) built for King Minos. In Greek mythology the minotaur was eventually killed by Theseus.

"Minotaur" is Greek for "Bull of Minos".

Firstly, King Minos built the maze below his palace. Secondly, the Minotaur came into existence when King Minos asked Poseidon for a bull for sacrifice. When the bull came out of the sea, Minos took it and thanked Poseidon a lot. But when Minos broke a vow that he'd made previously, the god made Minos's wife fall in love with the bull. She had an affair with it and out came the Minotaur. Minos was terrified and locked the beast away in the maze. Every nine years he would sacrifice children to the monster to keep it at bay.
GTB - Minotaur
Sleeping Ariadne
Achelous Recounts
The Minotaur