The Trident is a weapon that is featured in The Little Mermaid franchise. The Trident has three prongs, and appears to be made out of gold. It is shown to have vast magical abilities, and thus has been desired by both Ursula and Morgana. It serves as the personal weapon of King Triton, and only Triton or one of his descendants remove it from its resting place. (Although it should be noted that he most likely decreed this after Ursula stole it from the first film, as in the TV series, Urchin was able to lift the Trident out of its resting place at one point despite him not being related to Triton at all.) Once it has been removed, there seem to be no limits on who can use it. It can even be used against the royal family, seen when Ursula misuses its powerful lightning bolts (meant to defend Atlantica) to instead try to murder Princess Ariel just for fun. According to the stage version of The Little Mermaid, Triton inherited the Trident from his father, Poseidon. There is a similar Trident in Sofia The First, wielded by the mermaid Queen Emmaline to stir up a typhoon to sink the yacht of Sofia's family.
In Kingdom Hearts, King Triton is the wielder of the trident. He uses its power to destroy Screwdivers, which attempt to enter the castle, in one instance, and then to destroy the Crystal Trident, which is actually the key to revealing Atlantica's Keyhole. Ursula eventually steals King Triton's Trident, and, like the movie, grows to a gigantic size. Sora and co. defeat her, and then they use the Trident as a replacement for the Crystal Trident to seal the keyhole.
There are also markers along the walls in Atlantica that points to the Palace that are in the shape of the Trident.
The story starts out with Sora, Donald, and Goofy meeting Ariel as she is swimming past them carrying the Trident. She tells them to not tell anyone that they saw her. Sora and co. enter the palace and find that the Trident was stolen and that Ariel has gone missing.
Later, Sora and co. find out that Ariel stole the trident but only to help Flounder who had been lost in the surface world. Ariel was going to give it to Ursula she said that giving her the Trident was the only way to save Flounder. They all traveled to Ursula's Lair, finding that she kidnapped Flounder as a way to get the Trident, which Ariel gives over to save Flounder.
In the end, Ariel reclaims the trident and Sora suggests that she should say she found the Trident and got it back all by herself. However, she says she can't do that because it was her mistake which she made to help her friend. She wants to tell the truth when she returns the Trident.
In Kingdom Hearts II, the Trident only appears in scenes with Triton and the song-battle against Ursula, where she uses it as a weapon once again. During the battle, Ursula uses it to deflect Sora's attacks and to attack Sora, Ariel and the others. At the end of the song, Sora successfully knocks the Trident out of Ursula's hands, and it lands in Prince Eric's boat. Eric then uses it as a javelin to defeat Ursula once again. The trident is last seen being used by King Triton to light the palace chandelier during the "A New Day is Dawning" musical.
The trident is shown to have various applications, depending on the will of the user. When its power is activated, it illuminates with a bright, shining golden glow (green in Morgana's case) and is heard to make a deep humming sound punctuated with high-pitched melodious tunes. Since whoever wields it has command over the oceans, it affords tremendous power.
Most commonly seen is its ability to fire destructive energy bolts. These energy bolts, however, must be fired immediately upon the ready, or they will cause the built up energy to backfire on the user. This is ultimately how Ursula was killed, as she attempted to fire an energy ray at Ariel that was implied to be unavoidable, but was impaled seconds before she could fire by Prince Eric and one of the ships, causing the energy to backfire on her. Though these energy bolts may destroy many things, the Trident is incapable of destroying or undoing Ursula's deal with Ariel.
Triton has also used it to summon rain storms, and transform his daughter, Ariel, into a human. He is also seen creating a rainbow in the first film, and disintegrating the sea wall in the second film. Ariel uses it herself in one episode of the television show, to thaw dinosaurs that have been trapped in a glacier, and it is revealed that the Trident is activated simply by the will of the user. When the trident is in Ursula's possession, she creates a giant whirlpool in the ocean that has such force that it raises sunken ships from the ocean floor.