In Greek mythology, Arcas (//; Ἀρκάς) was the son of Zeus and Callisto. Callisto was a nymph in the retinue of the goddess Artemis. As she would not be with anyone but Artemis, Zeus cunningly disguised himself as Artemis and seduced Callisto. The child resulting from their union was called Arcas.
Hera became jealous, and in anger, transformed Callisto into a bear. She would have done the same or worse to her son, had Zeus not hidden Arcas in an area of Greece that would come to be called Arcadia, in his honor. There Arcas safely lived until one day, during one of the court feasts held by king Lycaon (Arcas' maternal grandfather), Arcas was placed upon the burning altar as a sacrifice to the gods. He then said to Zeus "If you think that you are so clever, make your son whole and un-harmed." At this Zeus became enraged. He made Arcas whole and then directed his anger toward Lycaon, turning him into the first werewolf.
After this occurrence, Arcas became the new king of Arcadia, and the country's greatest hunter. One day when Arcas went hunting in the woods, he came across his mother. Seeing her son after so long, she went forth to embrace him. Not knowing that the bear was his mother, he went to kill her with an arrow. Zeus, taking pity upon the two, decided to avert the tragedy and put them both up in the heavens, and their constellations are now referred to as Ursa Major and Ursa Minor, the big and little bears. When Hera heard of this, she became so angry that she asked Tethys to keep them in a certain place, so that the constellations would never sink below the horizon and receive water.
Arcas was remembered for having taught people the art of weaving and baking bread. He was married to either Laodamia (Leaneira), daughter of Amyclas; Meganeira, daughter of Crocon; the nymph Chrysopeleia; or the Dryad Erato. He also left a number of children, including the sons Apheidas, Elatus, Azan and Triphylus, also an illegitimate son Autolaus and at least two daughters, Hyperippe and Diomeneia.