Poseidon

Neptune was king of Earth's oceans. He and his mermaid servants lived in a castle made of sand located on a South Seas island. After sending a wave to move the First Doctor, John and Gillian out of the way of a volcanic eruption, he gave them a great feast. Before they left, he gave a pearl necklace to Gillian and a golden shell to John. (TVC: Guests of King Neptune)


 * King Neptune may have been connected to the Immortals who posed as other Greek gods.