Poseidon

Poseidon is the Greek God of the Sea.

While many other Olympians have important functions, Poseidon just is. The seas would continue to exist even if he went away. He is simply a part of the ocean that has a will of its own.

He rarely has anything to do with his fellow gods. Hades and Demeter in particular are annoyed by him, as Poseidon sometimes causes earthquakes to remind landlubbers of his power, and both these deities have a far more responsible approach to the whole chthonic business.

For his part, he has a dislike bordering on hatred for Athena. For incomprehensible reasons, mortals seem to prefer her to him.

In short, Poseidon is a selfish brute, quite useless for anything else than terrorizing mortals. Included among his victims are Cecrops and Ulysses.