Sheldon J. Plankton

Sheldon J. Plankton is the main antagonist of the popular cartoon series SpongeBob SquarePants and its first film, The SpongeBob SquarePants Movie. But despite being an antagonist in the series and the movie, he had a role as an anti-hero in the sequel, The Sponge Out Of Water. He is an evil zooplankton and the business rival and personal archenemy of Eugene Krabs, the owner of the Krusty Krab where SpongeBob SquarePants works. While the Krusty Krab is popular among the sea creatures of Bikini Bottom, Plankton's own restaurant, the Chum Bucket, has very few customers. Plankton's plans all revolve around stealing the elusive "Krabby Patty Secret Formula" so he can copy it and make the Chum Bucket popular. He lives inside his restaurant, where he has an elaborate laboratory and a computer "wife" named Karen. He is voiced by Doug Lawrence.

As a matter in fact, in SpongeBob SquarePants. He's SpongeBob's baddest villain.

Series
Plankton constantly attempts to steal the formula for the Krabby Patty, the delicious burger-like food that is sold in the Krusty Krab. Plankton believes that the Krabby Patty is the reason for the Krusty Krab's success, and that his Chum Bucket would be equally popular if it sold the Patties as well. However, ensuring the success of his business is only the first step in Plankton's plan, which will culminate in him ruling the ocean.

Movie
In The Spongebob Squarepants Movie, Plankton does finally manage to steal the formula from Krabs, and the Chum Bucket becomes just as popular as the Krusty Krab had been previously. He even comes close to his eventual goal of ruling the sea, by giving away mind-controlling bucket hats free with his Krabby Patties, turning Bikini Bottom into "Planktopolis". He is eventually thwarted by Spongebob when he sings the "Goofy Goober Rock" to remove the bucket helmets from all the fish.

Sequel
He appears in the sequel as the secondary antagonist later anti-hero then back again and helps Spongebob, Patrick, and the others get the formula back from Burger-Beard.

Battle For Bikini Bottom
In this game, Plankton creates an army of robots to take over Bikini Bottom, but forgets to make them obey him, causing his creations to run amok across the seabottom. Plankton uses SpongeBob, who is convinced that he caused the robot invasion while role-playing with Patrick, to get rid of the robots, which are led by a robotic version of Plankton.

Nicktoons Unite!
Plankton is one of the villains who compose The Evil Syndicate, the main antagonists of the game. He was charged to harvest energy out of the jellyfishes in Jellyfish Fields for the Doomsday Machine the Syndicate was building, making changes in the Chum Bucket to make it a factory. He aso began to kidnap citizens of Bikini Bottom (including Patrick) who didn't go along with his plans. However, the group of heroes assembled by Jimmy Neutron, Spongebob included, managed to free the jellyfishes and defeat Plankton at the Chum Bucket. He retreated to Retroville were he tried to destroy the heroes along with his fellow Syndicate members. But even that failed as his shield was turned off and he was defeated again by Spongebob.

Nicktoons: Globs of Doom
Plankton returns in this game as the only original member to be part of the second Syndicate. He, along with other villains, join forces with the heroes to gather parts for the Vessel of Portentia and defeat the Morphoids. However, he also betrays the heroes at the end when they are about to defeat Globulous Maximus and the villains steal the Vessel. However, he and the others were defeated when Maximus takes them one-on-one at the moon, destroying the Vessel and leaving them in the vacuum of space.

Personality
Plankton is an evil mastermind through and through. His plans always involve technological devices and weapons, all for the sake of the formula. His main goal has always been throwing the Krusty Krab out of business. In Seasons 1 to 5, he was completely unable to get any success for his Chum Bucket restaurant. However, in the movie and later seasons, he was now able to get more chances of success other than stealing the Krabby Patty formula, such as having an attractive restaurant place where the people will come to observe the beauty of. Other examples are putting slogans such as "Chum is Fum" and "Fum is Chum" and one person named Nat Peterson kept coming to buy chum to eat, although he was only doing it since Karen paid him to do so.

Trivia

 * Plankton found Mr. Krabs' life to be worse than his life (because Plankton ruins Mr. Krabs' life), when he experienced it in The Algae's Always Greener and Spy Buddies. In The Algae's Always Greener, he found lots of reasons that make Mr. Krabs' life difficult:
 * Spongebob is always asking him for a Weekly Performance Review on Tuesday and makes a teensy little temper tantrum if Plankton refuses. He also keeps yelling "SOILED IT! SOILED IT! SOILED IT!" when he accidentally gave a customer a large soda when the customer wanted a medium soda.
 * Squidward, the lazy grumpy pessimistic worker at the restaurant, complains to Plankton that he doesn't want to work with SpongeBob. Later, when Plankton put him in charge of fry cooking, a customer got angry because the Krabby Patty that Squidward cooked was very ugly, disgusting-looking, and hideous.
 * Pearl, his virtual reality daughter, throws a big temper tantrum because she doesn't get more than $1.
 * Krabs tries to steal the Krabby Patty formula (which Plankton actually does in the show's reality), and Krabs NEVER gives up.
 * In the movie Plankton is a lot more evil and depraved than he was in the series. While in series he was comical and in post movie episodes became less evil (while Mr. Krabs has gotten more greedy and evil), but in the movie he stole King Neptune's crown, frames Mr. Krabs for it, enslaves Bikini Bottom, shows excitement and joy when Mr. Krabs is going to be killed and sends Dennis to kill SpongeBob and Patrick rather than merely get rid of them. He was claimed to be the main antagonist in the sequel, The SpongeBob SquarePants Movie: Sponge Out of Water, but this was a misinformation campaign to hide the true main villain.
 * Plankton will team up with Terry Silver in Pooh's Adventures of The Karate Kid, Part III.
 * Plankton almost had his revenge on SpongeBob and Patrick in Winnie The Pooh In Fantasmic!.
 * Plankton will become a new member of The Masters of Evil in Winnie the Pooh Gets Frozen.
 * Plankton will get his revenge on Pooh and his friends in Pooh's Adventures of The SpongeBob SquarePants Movie.
 * Plankton will get his revenge on Simba and the gang in Simba, Timon, and Pumbaa's Adventures of The SpongeBob SquarePants Movie.
 * Plankton will get his revenge on Littlefoot and his friends in Littlefoot's Adventures of The SpongeBob SquarePants Movie.
 * Plankton will become the enemy of Thomas, Twilight, and their friends in Thomas and Twilight Sparkle's Adventures of the SpongeBob SquarePants Movie.
 * Plankton will make his first guest appearance in a Madagascar crossover in Alex's Adventures of Peter Pan, where he'll team up with Makunga to work for Captain Hook.
 * Plankton will become an enemy of Bloom and her friends in Pooh's Adventures of Winx Club Season 2.
 * Plankton will get his revenge on Bloom and her friends in Bloom's Adventures of The SpongeBob SquarePants Movie.
 * Plankton will return again in Pooh's Adventures of Avatar and the Winnie the Pooh/SpongeBob SquarePants short films.