The Cretan Bull
It was a handsome bull sent forth from the sea by Poseidon. Queen Pasiphae of Crete lusted after the animal and coupled with it by hiding inside a wooden cow crafted by the Daedalus. She later gave birth to the Minotaur, a man with the head of a bull.
Heracles was commanded to fetch the Cretan Bull as one of his Twelve Labours. Upon completion of this task, he set the creature free and it eventually found its way to the Athenian town of Marathon where it laid waste to the countryside. There it was finally destroyed by the hero Theseus.
Killed by: Theseus
It was a monster born with the foreparts of a black bull and the tail of a serpent. It was slain by a giant ally of the Titans, who hoped to sacrifice its guts in a rite which would have ensured victory against Zeus. However the god’s kite stole the parts away, thwarting the plan.
Killed by: Aegaeon