Neleus is the son of Tyro and Poseidon, exposed with his twin brother Pelias by his step-father King Cretheus of Iolcus. Though twins, Neleus is physically and intellectually inferior to his brother. More than once in his life Neleus is saved by his Pelias. His nature is more amicable, submissive and pacific than his brother, stemming from a different reaction to peer pressure as a youth, a dependency on Pelias and an acknowledgment of his own inadequacy. Even after marrying a Theban princess, Chloris, daughter of Amphion and Niobe

Neleus often acts ill-advisedly and with poor consideration, a flaw that almost costs him his life when he informs Pelias that his eldest daughter Pero is due to be married to King Bias of Argos. The consequences force him to flee Iolcus and seek refuge in southern Greece with his wife and expanding family. His amicable nature is tested by Pelias' treachery and a continual lack of charity from the royal houses of Greece. After wandering from city to city he eventually settles in Pylos in the Peloponnese. There his family grow to adulthood, including two sons of particular note - Nestor and Periclymenus.

Neleus' hardened heart costs himself and his sons their lives in later life, with Nestor the sole survivor of a devastating attack on his house.