Poseidon

Poseidon is the Olympian god of the seas and the older brother of Zeus and Hades. Despite his small role in the film, he plays a larger role in the animated series. He is voiced by Jason Alexander.

Hercules (film)
In the film, he is present for the party celebrating the arrival of Zeus and Hera's newborn child, Hercules. Eighteen years later, Poseidon and his fellow gods are imprisoned by Hades and the Titans. He and the other gods are freed by Hercules.

Hercules (animated series)
In the animated series, Poseidon plays a much larger role than in the movie, either by acting as a major part in the plot or by appearing in a cameo.

In this episode, Poseidon is visited by his youngest brother, Hades, who tries to trick him into using his powers to move the River Styx (a part of Hades' domain) into Greece (a part of Zeus' domain). Such a ploy would place Greece in Hades' control, therefore making him the ruler of Olympus. In exchange, he promises to give Poseidon the city of Athens. Poseidon introduces Hercules to his son, Triton (Chris Elliott), a sea prince who wants to go to Prometheus Academy with him. It turns out Triton is somewhat of a nerd, wanting to be like his cousin; he has considerable acrobatic skills but terrible balance and timing, much like Hercules himself, causing him to be a constant source of humiliation. Icarus and Cassandra remind Hercules that he and his cousin are not so different, so he tries to apologize. Unfortunately, having overheard what his cousin thought of him, Triton steals Poseidon's trident and accidentally unleashes a sea monster. The two cousins team up to defeat the monster, and Poseidon arrives to retrieve his trident, not punishing Triton due to Amphitrite intervening. Poseidon, tired of being forgotten, holds a boating race in his honor with Adonis competing for Thrace against Hercules and Icarus. However, when their star rower Hylas (Rocky Carroll) is injured, the King of Thrace hires Hercules instead, who abandons Icarus. Fortunately, Amphitrite (Leslie Mann), the wife of Poseidon, has taken a special interest in Icarus and helps both him and his father, Daedalus, in completing their boat. At a regala held the night before the race, Hercules declares himself bigger than Poseidon, which causes the sea god to unleash Charybdis, a giant maelstrom sea creature, during the race, which causes both his and Icarus' ships to nearly sink. Rescuing first his friend and then Adonis, Hercules looks on as Icarus wins the Poseidon Cup, being the only one to have truly earned it.
 * Hercules and the River Styx
 * Hercules and the Son of Poseidon
 * Hercules and the Poseidon's Cup Adventure

Powers and abilities
Poseidon is a very powerful god and only second to Zeus in power.
 * As an Olympian god, Poseidon possesses natural powers and abilities such as immortality, omnipresence, omniscience, superhuman strength, metamorphosis, and teleportation
 * As the god of the sea, Poseidon possesses the abilities to breath underwater, to communicate with sea creatures, and to control the sea with his Trident. Being the lord of the sea, Poseidon has authority over it and its creatures.

Trivia

 * Poseidon has a son named Triton, which is also the name of Ariel's father, the ruler of Atlantica and king of the seven seas, in Disney's The Little Mermaid.