Hades

In Mythology: Hades was the ancient Greek god of the underworld. He is also the oldest child of Kronos and Rhea. He is often pictured with the three-headed dog Cerberus. In the later mythological tradition, he is associated with the Helm of Darkness and the bident. He is most famous for abducting the goddess of spring Persephone and making her be his wife.

In the book: In the book is is most known for abducting Percy's mother in the first book while trying to get back his Helm of Darkness which was stolen from him at the same time that Zeus's bolt was taken from him. He is also the father of Nico di Angelo one of the main  characters in the book. 

If you would like to know more about Hades please go to this link:
www.greekmythology.com/Olympians/Hades/hades.html

                                             Hephaestus

In Mythology: Hephaestus is the God of fire and blacksmiths. He is the son of Zeus and Hera but was thrown off of Olympus because he was ugly. He is most famous for crafting lighting bolts for Zeus.

In the book: He is not featured much in the book however he did craft the item needed for Percy and Annabeth to navigate the Labyrinth. And he also helped Percy  get of Calypso's island at the end of book four.

If you want to learn more go to this link: http://en.wikipedia.org/wiki/Hephaestus

                                     Hermes

In Mythology: Hermes is an Olympian god in Greek religion and mythology, son of Zeus and the Pleiad Maia. He is second youngest of the Olympian gods. Hermes is a god of transitions and boundaries. He is quick and cunning, and moved freely between the worlds of the mortal and divine, as emissary and messenger of the gods, intercessor between mortals and the divine, and conductor of souls into the afterlife. He is protector and patron of travelers, herdsmen, thieves, orators and wit, literature and poets, athletics and sports, invention and trade.In some myths he is a trickster, and outwits other gods for his own satisfaction or the sake of humankind. His attributes and symbols include the herma, the rooster and the tortoise, purse or pouch, winged sandals, winged cap, and his main symbol is the herald's staff, the Greek kerykeion or Latin caduceus which consisted of two snakes wrapped around a winged staff.

In the book: He is the father of Percy's enemy Luke and has helped Percy throughout the entire series including giving him extra supplies for many of his adventures including his adventure to get the golden fleece in the Sea of Monsters.

If you want to learn more about Hermes please go to this link

 www.pantheon.org › Areas › Mythology › Europe › Greek mythology‎

                                    Hera

In mythology: In Greek mythology Hera was the Goddess of women and marriage as well as the queen of Olympus. She is the sister of her husband Zeus and mother of many of the Gods such as Ares and Hephaestus. She is most well known for her involvement in the Trojan War as well as giving Hercules his twelve labors for being Zeus's son.

In the book: In the book she is a very minor character only being involved in Percy's life by hating him and Annabeth. And by telling Annabeth in the Labyrinth that she has to make a big choice soon.

To learn more about Hera go to this link www.greekmythology.com/Olympians/Hera/hera.html

                                         Zeus

In mythology: In Greek mythology Zeus was the God of the sky and the king of Olympus. He was married to his sister Hera and brother of Poseidon and Hades. He is also the son of the Titan lord Kronos who he had overthrown. He is also the father of other well known Greek legends such as Ares, Hercules, and Perseus.

In the book: In the series Zeus is not a major player in Percy's life after the first book. In the first book his lightning bolt was stolen causing Percy to discover that he was a demigod. He is not featured until the final book in the series where he offers Percy the chance to become a God for his success at saving Olympus, which he refuses.

If you want to learn more about Zeus please go to this link www.greekmythology.com/Olympians/Zeus/zeus.html