Apollo chased the nymph Daphne ("laurel"), daughter of Ladon, who had scorned him. His infatuation was caused by an arrow from Eros, who was jealous because Apollo had made fun of his archery skills. Eros also claimed to be irritated by Apollo's singing. Daphne prayed to the river god Peneus to help her and he changed her into a laurel tree, which became sacred to Apollo.
Apollo and Daphne by Gian Lorenzo Bernini, depicting the moment of Daphne's transformation into a laurel tree