Nereus

"He will smell...different."

- Zoë Nightshade

Nereus (Νηρέας in Ancient Greek) is the "Old Man of the Sea" and apparently knows everything, even things concealed from the Oracle of Delphi. Not much is known about his past, though he claims to have existed before Poseidon, whom he calls an "upstart", stating I was here first! If captured, he will allow his captor to ask him one question. He can shape-shift into practically everything, including inanimate objects (though in his appearances in the series he only becomes aquatic animals such as a seal, an electric eel, and a killer whale).

History
Nereus, a sea-deity, was son of Oceanus, by Tethys. Apollodōrus gives him Terra for his mother. His education and authority were in the waters, and his residence, more particularly, the Aegean seas. He had the faculty of assuming what form he pleased. He was regarded as a prophet; and foretold to Paris the war which the rape of Helen would bring upon his country.

When Heracles was ordered to fetch the golden apples of the Hesperides, he went to the Nymphs inhabiting the grottoes of Eridanus, to know where he might find them; the Nymphs sent him to Nereus, who, to elude the inquiry, perpetually varied his form, till Hercules having seized him, resolved to hold him till he resumed his original shape, on which he yielded the desired information.

Nereus had, by his sister Doris, fifty daughters called Nereids. Hesiod highly celebrates him as a mild and peaceful old man, a lover of justice and moderation.

The Titan's Curse
Following advice from Apollo, Percy Jackson found Nereus at the beaches in San Francisco, California, and fought him through the water, as the only way to get a question out of Nereus was to hold on to him no matter whatever happened. During the fight, Nereus shape-shifted into different types of animals, including a a seal, orca, and goldfish to shake off Percy's grasp. However, his tossing and shape-shifting didn't work well because Percy held onto him all the way through. Nereus was obviously tired of this way of life and just wants to be left alone. However, Percy tricked Nereus into jumping into the water with him holding on, making Percy stronger and overpowering him. Nereus was confused as to why Percy didn't drown at all, and Percy revealed that he was a son of Poseidon, much to Nereus' dismay. He eventually conceded the struggle and agreed to answer the heroes' question. Percy asked him for the location of the monster that Artemis, goddess of the moon and the hunt, had been tracking. Nereus said that the question was too easy and simply pointed to the Ophiotaurus, the creature that had been following Percy and his friends during the events of their quest. Soon after, Nereus escaped Percy's grasp got away.

The Son of Neptune
When Percy, Hazel, and Frank are sailing out of San Francisco Bay, Hazel becomes so sea sick that she thinks she is hallucinating when she sees him as an old homeless man hanging around a bunch of sea lions. When he sees Percy, he remembers their previous encounter, and points his finger at Percy as if to say, Don't even think about it.

Appearance
Nereus is described as looking like Santa Claus's evil twin, fat and having a white beard that turned kind of yellow. Nerues was wearing pajamas and a fuzzy bathrobe. He is also described as having a bad smell, like hot seaweed, dead fish and brine. Percy said that "If the ocean had an ugly side, this guy [Nereus] was it."

Abilities

 * Able to change shape into aquatic animals (in The Titan's Curse he changed into a seal, killer whale, eel, and goldfish while fighting Percy).
 * Extensive (possibly unlimited) knowledge, including things unknown to the Oracle of Delphi.

Children

 * With the Oceanid Doris:
 * Delphin
 * Glaucus
 * Nerites
 * The Nereids, Amphitrite, Thetis, Psamathe, Galatea, Ploto, Thoe, Sao and others.