The Taurus myth is most often interpreted as the story of Zeus and Europa, where the Greek god carried the Phoenician princess away to Crete to marry her by disguising himself as a white bull. Then I guess the bull, that was really Zeus, became the Taurus constellation, but not really, because now the bull and Zeus are different... or something.
An alternate myth gives us another possible explanation of the Taurus constellation, one that I find a bit more satisfying.
According to this myth, the mythology of Taurus begins with a wandering bull known as Cerus. Cerus was a large and powerful bull who villagers were terrified of because of his tendency to trample their villages to pieces on a whim. He was owned by no one, and none of the farmers knew where he came from. Though he was not immortal, most people assumed him to be because of his sheer size and strength and the fact that despite all of the destruction he caused nobody was ever able to stop him.
The bull is wild and out of control, choosing to follow his emotions on a whim. One day the Spring goddess Persephone finds him trampling through a field of recently-bloomed flowers and goes to him. Though he cannot speak, he seems to understand her and her presence calms her. They form a bond together, and the bull learns to behave himself. Persephone teaches the bull patience and how to use his strength wisely.
After In fact, every year in the spring when Persephone returns to the land, Cerus returns to the land to join her. She sits upon his back and he runs her through the fields, allowing her to set all of the plants in bloom as they ride by. In the fall when Persephone returns to Hades, Cerus returns to the sky as the Taurus constellation.