King Neptune, born over 5,000 years ago, is the series' depiction of Neptune, the Roman god of the sea. In the SpongeBob SquarePants universe, Neptune is the god and supreme ruler of the sea. His name is often used in place of God's, with phrases such as "Dear Neptune," "Neptune preserve her!," and "Oh my Neptune!" However, he has never explicitly been shown to be worshiped by the creatures of the sea.
King Neptune is a regal king who has a strong opinion of his rank as a deity and is known for using his powers to bully mortals and punish them for talking back to him. He often judges people for their sizes and thinks a person with a grand physical appearance is worthy of him. At first, he imprisoned Triton for wanting to help mortals, but then he eventually welcomed Triton back into the family after SpongeBob freed him.
In The SpongeBob SquarePants Movie, he tried to kill Mr. Krabs when he was falsely accused of stealing his crown, with no evidence that Krabs stole it aside from a false call made by Sheldon J. Plankton. He also kept Mr. Krabs frozen for days and nearly killed him after having his stalling daughter left. He almost nearly sent a royal crown polisher to the dungeon for 20 years for touching his crown (even though it was his job) and threatened to burn SpongeBob along, after he disagrees with him about letting him go to Shell City to get the crown back.
In "Neptune's Spatula," he keeps thinking SpongeBob is just a joke, and can't pull out the spatula. He then becomes destructive and repeatedly burns Patrick, only to fix him later, albeit incorrectly with his face on his butt.
In "The Clash of Triton," when Neptune's son Triton does not want to be a god like his father and wants to use his powers to help people, Neptune locks him in a cage in the Island in the Sky until he learns how to be a proper god like his father. He only ends up accepting Triton after he wrecks the town.
King Neptune first appears in the season 1 episode "Neptune's Spatula," where he spawns after SpongeBob pulls the golden spatula from the ancient grease, making him Neptune's royal fry cook. However, Neptune refuses to accept such a lowly creature like SpongeBob as the chosen one and challenges him to a cook-off where, if the latter wins, he will become a god in Atlantis, but if he loses, he must give up fry cooking forever. The challenge is held at the "Poseidome," where the first one to make 1,000 patties wins. Using his godlike powers, Neptune wins the challenge just as SpongeBob finishes his first patty. To celebrate his victory, he gives the patties to the audience, who hate it. Neptune then tastes SpongeBob's patty and loves it. He declares SpongeBob the winner and makes him a god. However, when SpongeBob learns that his friends can't join him in Atlantis, he does not want to go and instead, makes Neptune his "trainee" at the Krusty Krab. In the show, Neptune is green and has fairly realistic human features, has hair, a mustache, a beard, thick fingers, is very muscular, and has a different crown. This version of Neptune also appears in Battle for Bikini Bottom, where he summons SpongeBob and Patrick to the Poseidome to defeat a robot version of Sandy.
Neptune plays a central part in The SpongeBob SquarePants Movie. The movie also introduces Neptune's daughter, Princess Mindy. In the movie, Neptune is bald, has brighter green-skin, has a larger nose, and a different beard. He is also explicitly portrayed as a king rather than a god and lives in some sort of sand castle just outside of Bikini Bottom somewhere in Atlantis. Neptune is very cruel, brutish, and tyrannical, which he tells his daughter is necessary for him to be a respected ruler. Neptune is shown to be a ruthless and unfair deity who rules over the sea with an iron fist and making his citizens suffer constant harsh punishments (including sending his servant 20 years in the dungeon for touching his crown, even though it's his job to polish the crown). His crown is very important to him, not only because it is a symbol of his power, but because it covers his "thinning" (bald) head. When the crown is stolen by Plankton, Neptune attempts to execute Mr. Krabs, who is framed for the crime with the only evidence being a fake note saying he did it and a phone call by Plankton saying he took it to Shell City. When SpongeBob refuses to let him kill his boss, he threatens to fry him along with his boss until Mindy arrived and convinced her father to let him go to Shell City and get his crown back, leading to Neptune to angrily order SpongeBob to return with the crown in 6 days(which was originally 10 until Patrick argued it down to 6) and freezes Mr. Krabs, as he will keep him that way until the day of execution. He spends the rest of the movie dealing with his bald spot (as shown through Mindy's magical clam) while Bikini Bottom has been taken over by Plankton and Neptune doesn't even care. He then realizes the error of his ways at the end of the movie when he nearly kills Krabs after he magically locks his daughter out of the restaurant for stalling him, before SpongeBob and Patrick arrived with his crown before he does so. Happily reunited with his crown and praising SpongeBob for his heroic deed, he finally takes Mindy's advice of being a loving and compassionate ruler and apologizes to Mr. Krabs for freezing him.
In "SpongeHenge," Shubie denies Neptune's existence when an anchovy tells her that Neptune must be mad, saying "Everyone knows Poseidon is the ruler of the undersea."
A picture of King Neptune, as seen in "Neptune's Spatula," is shown in "Krusty Towers." Squidward refers to this Neptune as "Neptune XIV."
In "The Clash of Triton," the version of King Neptune from "Neptune's Spatula" appears with John O' Hurley voicing him once more. It's his birthday and he's spending it at the Krusty Krab, but he can't enjoy himself because he misses his son, Triton too much. He imprisoned his son for thousands of years because he wanted to To cheer Neptune up, SpongeBob and Patrick go to the prison where Neptune trapped Triton years ago. The boys free Triton and Triton begins to take his revenge on Neptune by trapping him in the same cage and wreaking havoc on Bikini Bottom. SpongeBob saves Neptune and the king goes to confront his son on his actions. However, when Neptune sees that Triton used his powers at long last, he accepts Triton for who he is, and the two return home, now closer than ever.
"Trident Trouble" marks King Neptune's first speaking appearance since "The Clash of Triton." SpongeBob accidentally gets ahold of his trident and Neptune gets SpongeBob's spatula, causing trouble. Eventually, Neptune realizes the mixup and is defeated by a monster. Neptune appears in the city and points out the error to SpongeBob before giving the trident back. Neptune didn’t dissolve the sponge is damage to the town. They team up to defeat the monster and her child with a monster patty.
Neptune appears in "High Sea Diving." At the very end of the episode, he appears in Bikini Bottom and was angry at Old Man Jenkins for tricking the town with his made-up stories and impersonating him. As punishment, Neptune then zaps the deluded and now scared old man with his trident.
Employee of the Month - An amusement park called Neptune's Paradise is a destination for SpongeBob and Patrick.
Battle for Bikini Bottom - King Neptune invites SpongeBob and Patrick to the Poseidome to face off against a giant Robo-Sandy which they manage to defeat.
The SpongeBob SquarePants Movie (video game) - King Neptune's role is the same as in the Movie: his crown goes missing and he accuses Mr. Krabs of taking it. He later sends SpongeBob and Patrick to find it, allowing Plankton to take Bikini Bottom for himself. His crown is returned and he frees Mr. Krabs. Under the control of Plankton, he is the final boss of the game.
SpongeBob's Atlantis SquarePantis - King Neptune makes a cameo in a painting in the Bikini Bottom Museum as an object SpongeBob must photograph. The painting is also unlockable in the gift shop with The Sirens added in it.
SpongeBob and the Clash of Triton - Triton, King Neptune's son, captures King Neptune on his birthday at the Krusty Krab. After his and Queen Amphitrite's tridents fall near SpongeBob and Patrick they gain powers and defeat Triton's underlings. They defeat Triton, restore Bikini Bottom to its former glory, and reunite Triton with his proud father.
King Neptune's redesign in The SpongeBob SquarePants Movie was due to a firewall between Nickelodeon and Paramount content at the time. This resulted in other elements created for the first movie not being allowed to be used in the series from 2005 to 2014.
The designs are even poked fun at in the 20th anniversary poster, where both Neptunes are glaring at each other.
Neptune usually has five fingers on each hand, although in some long shots, he has four like some other characters.