In one of his most popular incarnations, he is called the Hunter and, with his Hounds (Canes Venatici), he eternally circles the Bears, Ursa Major and Ursa Minor, around the North Pole. In fact, the brightest star in Boötes is Arcturus, which can be loosely translated as "Bear Guard."
He is also called the Herdsman and his journey around the pole represents his task of keeping the celestial beasts together.
Another legend says that Bootes was the son of Zeus and Callisto. Hera changed Callisto into a bear who was almost killed by Boötes when he was out hunting. Luckily, she was rescued by Zeus and he took her into the sky where she is now Ursa Major, the Great Bear.
Yet another myth says that he was the son of Demeter, the goddess of agriculture. Supposedly he was given a place in the sky for inventing the plow.