Together with the Little Bear and the Dragon, the Big Bear derives its name from the myth that focused on Chronus and his pursuit of his son Zeus and his "nurses". A prophecy of Chronus' parents Uranus and Gaia had in fact predicted that he would be dethroned by one of his children.
According to legend, the two bears took care of the infant god in the cave were he had been hidden, after escaping his father's attempt on his life.
A different myth says that Zeus fell in love with Callisto, a nymph of Artemis, who was to keep her vow of chastity, as were all the nymphs of Artemis. Zeus, though, took the features of Artemis herself to deceive Callisto, and forced himself upon her, after which they had a child called Arcas. Artemis, out of punishement for the broken vow, turned the nymph into a bear.
Another version attributes the transformation to Hera, out of jealousy, or to Zeus himself, wanting to hide his infidelity to his divine consort.
The bear was later killed either by Hera, who had discovered the deception and consequent disguise, or by Artemis, as extreme punishment. Yet a different version says that some years later Arcas, grown up into a skilled hunter, suddenly met her in a wood and killed her, not recognizing her as his own mother.
Zeus placed the Big Bear in the sky as a constellation while the desperate Arcas asked Zeus to transform him too, so that he became the Ursa Minor or Small Bear. According to another interpretation of the myth, Arcas became instead Bootes the herdsman, keeper of the seven oxen of Ursa Major.
For the Romans the constellation represents seven oxen plowing the starry sky, which appears as a field of wheat. Septem Triones in Latin means "seven oxen,", from which derives Septentrional (northern) which indicates the position of the constellation in the sky.