Because Zeus ordered her to release him by a message with Hermes.
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Athena (his patron goddess) asked Zeus to get Odysseus off the island. So Zeus sent Hermes to tell Calypso to let Odysseus free.
Odysseus met Calypso on her lush island of Ogygia.
I believe this is Calypso.
Circe, Calypso, Ino, and Nausicaa help Odysseus. Athena helps Odysseus as well.
Calypso appears in several films, most notably in the "Pirates of the Caribbean" series, where she is portrayed by Naomie Harris in "At World's End." Additionally, the character has appeared in various adaptations of Greek mythology, such as the 1997 animated film "Hercules" by Disney, where she is referenced in relation to Odysseus's journey. Other films may include interpretations of "The Odyssey," where Calypso is depicted as the nymph who keeps Odysseus on her island.
Calypso. She kept him for a number of years (7, I think) and granted him immortality while he stayed with her. She then allowed him to leave on a massive raft she provisioned. She also sent a following wind to take him on his way home.
Hermes rescues him. Zues sends him.
Calypso offers immortality to Odysseus
Hermes tells Calypso to let Odysseus go.
Odysseus met Calypso on her lush island of Ogygia.
Calypso
Calypso has the power of immorality over Odysseus.
Hermes is sent down to Calypso, telling her that the gods wish for her to release Odysseus. Therefore, it is Calypso who allows Odysseus to leave, not Odysseus who 'manages to say no.'
Calypso
Calypso and Odysseus become lovers. Calypso offers Odysseus immortality and eternal youth if he would stay with her. Calypso does not aid Odysseus' escape until told to do so, so he seemed trapped on her island without a ship.
Calypso wants Odysseus to stay with her on the island forever.
No! Poseidon tries to drown Odysseus during his escape from Calypso. Athena and Hermes assist Odysseus.
Calypso