In the original Greek myths Poseidon and Hades are Hercules uncles, like in the Disney reproduction. Theses characters resemble much of their mythological counterparts, with a few critical exceptions:
Hades often drew with his brothers Zeus and Poseidon for shares of the world. He ended up getting the worst end of the stick, his draw made him lord of the underworld. In his myths he is greedy, unpitying, terrible, and manipulative – much like in the Disney movie. The myths also spoke of Hades tendency to favor those who increase the amounts of deaths. He paid particular attention to the Erinnyes. There were three of them: Tisiphone, Alecto, and Megaera (the woman that Hercules falls in love with in the Disney movie shares this name – coincidence?). They pursued wrong does until death; they were often the cause for suicide – not directly related in the Disney movie. The Erinnyes were not represented in the movie, maybe because of the fact that they were violent and caused events that were less than favorable for a children’s movie, so instead Disney put the mythological creatures known as Fates at Hades right wing instead.
The Fates are three old sisters responsible for deciding one’s destiny. An intriguing aspect of them, which may have been influential in Disney’s choice to use these Greek Gods instead of the Errinyes, was that they shared a single eye. Clotho spins the thread of life, Lachesis measures the lot in life and determines how long their life will be, and Atropos cuts the thread of life at the individual’s death. Now this doesn’t exactly sound Disney, they’re responsible for death! But Disney has it’s way of making it more child appropriate, see this video.
Poseidon was the God of the sea and he protected all waters. He is known as the second strongest Greek God, next to Zeus. His weapon was a trident that could shake the earth and destroy any object. There is a myth that claims Poseidon once tried to woo Demeter and in his attempts he attempted to create the most beautiful animal – which turned out to be a horse. In the Hercules movie Poseidon’s presence isn’t greatly evident. But there were a few, minimal, important remarks between him and Hades that represents their quarrelling relationship.
The important temple on the Akroppolis, the Erechtheion stands on the mythical site that connects the sea god (Poseidon) and Athena for patronage over Athens. Poseidon was known to be greedy and quarrelsome when he tried to take over other Gods cities. During this contest between him and Athena, Poseidon struck rock with his trident, creating a spout of water. Athena defeated him in this contest by giving Athens an olive tree. The Athenians enclosed this sacred rock in the Erechtheion’s north porch.