Who is keeping Odysseus on an island when he begins?

Odysseus is kept on the island of Ogygia by the nymph Calypso. She has fallen in love with him and keeps him there for several years, offering him immortality if he stays. However, Odysseus yearns to return to his home in Ithaca and to his wife, Penelope. Eventually, the gods intervene, and Hermes is sent to command Calypso to let him go.