Radagast is one of the Istari who came to Middle-earth to help the inhabitants in their battle against evil. He neglected his task because he was enamoured by the beauty of Middle-earth's nature. Being a Maia of Yavannë, this isn't really strange. His name as Maia is Aiwendil, which means 'Bird-tamer' and he lived at Rhosgobel, near Mirkwood.