Proteus, more familiarly known as "The Old Man of the Sea," was a son of Poseidon, and gifted with prophetic power.
But he had an invincible objection to being consulted in his capacity as seer, and those who wished him to foretell events, watched for the hour of noon, when he was in the habit of coming up to the island of Pharos, with Poseidon's flock of seals, which he tended at the bottom of the sea. Surrounded by these creatures of the deep, he used to slumber beneath the grateful shade of the rocks.
This was the favourable moment to seize the prophet, who, in order to avoid importunities, would change himself into an infinite variety of forms. But patience gained the day; for if he were only held long enough, he became wearied at last, and, resuming his true form, gave the information desired, after which he dived down again to the bottom of the sea, accompanied by the animals he tended.
From: Berens, E.M. The Myths and Legends of Ancient Greece and Rome. New York: Maynard, Merril, & Co., 1880. Text in the public domain.