Which Olympian god delivers Zeus's message to Calypso?

Hermes delivers Zeus’s message to Calypso. In the Odyssey, Zeus sends the divine messenger to Ogygia with an order that Calypso must release Odysseus and allow him to continue his journey home.

Athena initiates the intervention by speaking for Odysseus at the gods’ council, but she does not carry Zeus’s command to Calypso. Hermes is the appropriate envoy because he serves as the herald and messenger of the gods, traveling between Olympus, the mortal world, and the Underworld.

Calypso has kept Odysseus on her island for years and wants him to remain as her immortal husband. Hermes explains that Zeus has decreed Odysseus must leave, even though Calypso is angry that the gods object to goddesses taking mortal lovers. She ultimately obeys and helps Odysseus build a raft.

Hermes appears several times in the Odyssey. Besides visiting Calypso, he gives Odysseus crucial help before the encounter with Circe and later escorts the dead suitors to the Underworld.