Neleus was the son of Poseidon and Tyro, brother of Pelias.
Tyro was married to Cretheus (with whom she had one son, Aeson) but loved Enipeus, a river god. She pursued Enipeus, who refused her advances. One day, Poseidon, filled with lust for Tyro, disguised himself as Enipeus and from their union was born Pelias and Neleus, twin boys. Tyro exposed her sons on a mountain and they were raised by a maid. When they reached adulthood, Pelias and Neleus found Tyro and killed her stepmother, Sidero, for having mistreated her. Sidero hid in a temple to Hera but Pelias killed her anyway, causing Hera's undying hatred of Pelias.
Neleus and Pelias fought for the crown, and Neleus was banished to Messenia, becoming King of Pylos. Heracles later asked Neleus to cleanse him of a blood-debt and was refused. Heracles killed Neleus' sons, including Alastor but excluding Nestor.
Ovid II, 689.
With Chloris, Neleus was the father of Pero, Alastor and Nestor.