Circe was renowned for her vast knowledge of potions and herbs; one of her Homeric epithets is polypharmakos (“knowing many drugs or charms”). Through the use of these and a magic wand or staff, she would transform her enemies, or those who offended her, into animals.
The best known of her legends is told in Homer’s Odyssey when Odysseus visits her island of Aeaea on the way back from the Trojan War and she changes most of his crew into swine. He forces her to return them to human shape, lives with her for a year and has sons by her, including Latinus and Telegonus. Her ability to change others into animals is further highlighted by the story of Picus, an Italian king whom she turns into a woodpecker for resisting her advances. Another story makes her fall in love with the sea-god Glaucus, who prefers the nymph Scylla to her. In revenge, Circe poisoned the water where her rival bathed and turned her into a dreadful monster.
Source: Circe – Wikipedia