In Greek mythology, the Cretan Bull was either the bull that carried away Europa or the bull Pasiphae fell in love with, giving birth to the Minotaur.
When the sun has reached the constellation of Taurus, it has passed over an area that the ancients referred to as the sea - the region from Capricorn to the region containing Aries. It was referred to as the sea due to the high concentration of constellations identified as sea creatures within it, Aries being identified as a flying ram who flew over the sea. Crete is in a direct line from the natural harbour of Argo, a direction which the shape of Argo's harbour, and surrounding coastline, requires that all ships initially take this course.
Apart from being a bull, Taurus contains a very bright and red star, meaning that many took it to be evil. Some forms of Greek mythology associated the constellation with the tame white bull, in some versions Zeus in disguise, that seduced Europa and took her to Crete (Minos), whereas others associate it with the white bull that fathered the Minotaur. The Cretan Bull which fathered the Minotaur was originally calm and sent from Poseidon, but the king (Minos) whom it was sent to fell out of favour with Poseidon, and so in some versions of the story, Poseidon made the bull angry.
The myth of Poseidon sending the bull (which seduced Minos' wife) may simply be an earlier version of the myth of Zeus seducing Europa, as in earlier Mycenaean times, Poseidon had significantly more importance than Zeus. The change of gods was due to the replacement of the Mycenean culture and religion, with a later one favouring Zeus. Poseidon and Zeus, which have the same etymological origin (Poseidon deriving from Posei-Deion which means Lord God, and Zeus deriving from Deus which also means God), may be the result of the parallel evolution of the same original God in separate cultures, one (Poseidon - who is also associated with horses) becoming associated more with the sea (due to change in the main source of trade), and thus eventually becoming noticeably different.
The Seventh Labour of Heracles
Heracles was compelled to capture the bull as his Twelve Labours|seventh task. He sailed to Crete, whereupon the King of Crete, Minos, gave Heracles permission to take the bull away, as it had been wreaking havoc on Crete. Heracles used a lasso and rode it back to his cousin, Eurystheus. Eurystheus wanted to sacrifice the bull to Hera, who hated Heracles. She refused the sacrifice because it reflected glory on Heracles. The bull was released and wandered into Marathon, becoming known as the Marathonian Bull.
Capture by Theseus
Androgeus, a son of Minos and Pasiphae, competed in the games held by Aegeus, King of Athens. He won all the games, so angering Aegeus that he had the young man killed (some legends claim that he was sent to confront the Bull itself). Devastated, Minos went to war with Athens and won. As punishment, the Athens|Athenians had to send several youths every year to be devoured by the Minotaur.
Aegeus' own son, Theseus, set to try and capture the Bull. On the way to Marathon, Theseus sought shelter from a storm in the shack owned by an ancient lady named Hecale. She swore to make a sacrifice to Zeus if Theseus was successful in capturing the bull. Theseus did capture the bull, but when he returned to Hecale's hut, she was dead. Theseus built a deme in her honour. He then dragged the Bull to Athens where he sacrificed it.
Theseus then went to Crete where he killed the Minotaur with the help of Minos' daughter Ariane.