He operates a struggling restaurant called the Chum Bucket, located directly across the street from the Krusty Krab. His primary goal in is to steal the Krabby Patty secret formula and put Mr. Krabs out of business. Plankton succeeds at stealing the recipe in the movie, but his goal of world domination is thwarted by SpongeBob. In "Friend or Foe," it was revealed that Mr. Krabs and Plankton were once were best friends, but a dispute over the Krabby Patty recipe ended their friendship.
Plankton, as his name suggests, is a tiny green plankton that can fit in the palm of one's hand. He has stubby appendages, and one yellow eye with a red pupil. He has long, thin antennae with small green spikes sticking out along them.
Sheldon J. Plankton was born the only known child of Mama and Papa Plankton, son of Grandma Plankton. He was born on November 30, 1942. This is also the birth date of his former best friend and current rival Eugene H. Krabs.
When they were kids, Plankton and Krabs were considered outcasts by other kids because Krabs was poor and Plankton was a nerd. When they discovered that money could bring them out of their poverty, they decided to make money selling hamburger patties, and set up a mini-restaurant in the local dump. At first, their burgers were not successful; the first of their patties was tried by Old Man Jenkins, who was knocked out by the contaminated burger. Plankton started complaining about how Jenkins had been old and not able to handle the patty. Offended by this, Krabs tried to take the recipe from Plankton to improve upon. Plankton wanted to do this himself, but he only ended up with the corner of the recipe, which read: "And a pinch of chum." Plankton stormed out of the restaurant, and went to create his own recipe, using only his memory, the corner of the recipe, and science. At school, Plankton tried to sell his chum burgers in a chum bucket and failed, when Krabs succeeded with his Krabby Patties, which he had created by accident when Plankton had slammed the door. Ingredients fell in the patty batter, thus creating the patty. Plankton later named his restaurant the Chum Bucket, after the secret ingredient of the original unsuccessful patty recipe. Mr. Krabs named his restaurant the Krusty Krab.
To this very day, Plankton has been single-mindedly obsessed with obtaining the Krabby Patty formula and running the Krusty Krab out of business. He often goes to incredible and ridiculous lengths to do so. In "SpongeBob's Last Stand," for example, he builds a massive highway that goes straight through Jellyfish Fields and over the Krusty Krab, leading right to his restaurant simply to do so.
In "Dunces and Dragons," it was implied that the fight between the Plankton and Krabs families began centuries ago when Plankton's evil overlord ancestor Planktonamor was vanquished by a Krabby Patty. Since there was not any feud between Krabs and Plankton in their early childhood, it is possible that these families settled their differences until the childhoods of Krabs and Plankton.
In a comic story, Krabs and Plankton are shown to have been college roommates. Their rivalry is shown to have been caused by a series of things, including Plankton being stepped on by Mr. Krabs (which didn't annoy him at all), being closed inside Mr. Krabs' book (which aggravated him a little), and Mr. Krabs going out with his date and Plankton's date (which started their rivalry). Since it was revealed in "Friend or Foe" that they were rivals earlier than college, this story is likely non-canon. Even in the present day of the series, Krabs and Plankton are occasionally shown to somewhat get along, such as in "New Leaf" and "Best Frenemies."
Later, when Plankton was an adult, he married Karen.
Plankton's restaurant, the Chum Bucket, has always been extremely unsuccessful, not only because of competition from the Krusty Krab and Plankton's rude and cruel treatment of the people in Bikini Bottom, but also due to the extremely poor quality of the food and Plankton's constant failure to clean the place up. As its name implies, the Chum Bucket serves chum-based foods, all of which taste terrible. In "Plankton's Regular", the Krusty Krab adds chum to its menu in an attempt to steal Plankton's single regular customer (who was in reality being paid by Karen to eat at the Chum Bucket and pretend to like the food there). The customer is disgusted by their chum, and says that it is the second foulest thing he has ever tasted (it can be inferred that Plankton's chum is the number one worst). This implies that chum is inherently disgusting, and cannot be made to taste good, although is shown to be false in the Season 7 episode "Greasy Buffoons." Plankton used excess grease from the Krusty Krab's grease trap that was dumped near the Chum Bucket, to make his sales skyrocket (although it is unknown if this made the chum taste good, as Plankton could have been lying, and his customers could have been tasting only the grease, as the flavor could have covered up the chum's flavor).
It should be noted that in real life, chum is made of grounded up fish parts that are inedible to humans, such as heads and guts, and is used as bait for sharks and similar creatures. This would mean that Plankton is killing fish (or at least collecting dead fish) and serving their remains to other fish. This has only ever been touched upon in "The Krabby Kronicle", where SpongeBob prints a story claiming this. However, SpongeBob was being tricked by Mr. Krabs into printing absurd lies to appeal to customers, so this story was supposedly false. It also possible, that in the alternate reality the show takes place in, chum might be made of something completely different (although still likely disgusting), like in the episode "Spongicus", Plankton named off many weird things that make up his chum, and fish parts was not on the list.
Plankton has no regular employees, and runs the Chum Bucket entirely by himself, although he spends most of his time in his laboratory, due to having no customers. Plankton only runs the restaurant only when he has potential customers. In addition, when he does have customers, he also uses artificially intelligent machines to cover the other positions.
Although it has been stated on multiple occasions that Plankton has never had a single customer, he has had brief success on several occasions, particularly in more recent episodes, such as "Spongicus" and "Chum Caverns". A fan once wrote to Stephen Hillenburg, questioning that, due to Plankton being a genius in the fields of robotics, inventions, and technology (including many other fields), why Plankton doesn't sell computers and the like instead of fast food (which would actually probably bring him much better success). Hillenburg answered this with that Plankton has never gone this route, simply due to him having never thought of it before, and also due to the fact that Plankton is slightly incompetent, and also that he has terrible communication skills, he would probably ignore the person's idea until the last minute.
Shower In A Can!
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Plankton's "wife" is his computer system Karen, even though neither of them fully consider the other their true soul mate, and their relationship is a very troubled one, although it was slightly mended by the events of the episode, Komputer Overload.
Being a microscopic organism, Plankton's biological family numbers in the thousands. In "Plankton's Army," he recruits his entire family to help him steal the formula, thinking them all to be criminal masterminds like himself. However, much to his surprise, his family consists entirely of uneducated, red-necked hillbillies. These Relatives include (but are not limited to): Clem, Zeke, Rufus, Jeke, Billy Bob, Billy Jim, Billy Billy Bo Billy Banana Fana Fo Filly Plankton, Doug Plankton, Enis, and Rainchild, the only ones named.
Aiding in crime (his chum was used by criminals as knock out gas and disguises, both for robbery.) - (Jailbreak!)
Plankton appears in most SpongeBob-related video games, usually as a major antagonist.
In Battle for Bikini Bottom, Plankton devises a plan to take over Bikini Bottom and obtain the Krabby Patty formula by creating a robot machine called the Duplicatotron 3000. However, the robots do not obey him and begin mindlessly rampaging across Bikini Bottom because he forgot to set the switch from "Do Not Obey" to "Obey". Plankton convinces SpongeBob and friends to defeat the robots (as SpongeBob believed that the situation was his fault) so that he can have enough time to fix the main Duplicatotron 3000 so he can take over the city by controlling the robot army.
In Lights, Camera, Pants!, Plankton appears as a playable character. In the game, he uses a robotic suit to act in the auditions (the parts that are played). In addition, the "Captive" role, as well as the auditions for it, take place in the Chum Bucket.
In Nicktoons Unite!, Plankton is one of the four main villains of the game. He uses a crab mech to fight the heroes.
In Creature from the Krusty Krab, Plankton is one of three playable characters, as well as the final boss of the game. He enlarges a Krabby Patty to massive size, only to have it come to life and begin chasing him. Eventually, Plankton enlarges himself to gigantic size, and begins rampaging across the city in pursuit of the giant patty. He is eventually defeated and reverted to his original size by Patrick, who was playing as his alter-ego Starfishman.
In SuperSponge, Plankton has a brief cameo, in which he yells at SpongeBob for stealing his time machine ("Blast you, SpongeBrat! You have found my secret time machine! Well, whatever you do, make sure you fill it up before you bring it back!").
In "One Coarse Meal," it is revealed that Plankton is afraid of whales, enough to go insane. The reason is that a pod of whales ate his ancestors (also because whales eat plankton). He also fears his plans failing so many times.
There is a running gag in many episodes where he appears in (including the movie) he is squished.
It was revealed in "Single Cell Anniversary," that Plankton is not actually green, his outfit is. Karen removes the green and we see an underwear clad pink plankton embarrassed of his nakedness. He also has a rack with identical green suits.
Plankton is left-handed.
Plankton and Mr. Krabs were born exactly the same date as revealed in "Friend or Foe."
Interestingly, although his name is "Plankton," he bears more resemblance to the real-life class of organisms, Copepoda (Cyclops), which feed on phytoplankton. Do note that plankton are known to come from a different Kingdom than Copepods.
Plankton should be able to remember the Krabby Patty Secret Formula from The SpongeBob SquarePants Movie, although Stephen Hillenburg said that chronologically, The SpongeBob SquarePants Movie is the last part of the series.
It seems odd that Plankton wants to steal the Krabby Patty Secret Formula and make money from it, and in fact succeeded in accomplishing both in the movie, when doing so should have led to him facing a lawsuit for plagiarism and/or copyright infringement. Perhaps Mr. Krabs, due to his miserliness, never bothered to copyright the formula, and thus, Plankton could steal it without running the risk of being sued.
Plankton is college educated, which has become a running gag throughout the series, as he would usually shout, "'I went to college!"
Steven Hillenburg says that chronologically, The SpongeBob SquarePants Movie is the series' end. However, in the movie Plankton says he's never had a customer, but in Chum Caverns and Chum Bucket Supreme, he has had at least, and usually more than his only competition, the Krusty Krab.
Out of his whole family, he seems to be the smartest, as his family is shown to be clueless and unintelligent.
His family is made up of hillbillies (or what they appear to be), and he appears to have forgotten their stereotype after all these years, as in their episode, he believes they are "criminal masterminds" and when he sees them, he is shocked and says "I've been away from home longer than I thought." It is possible that after this, he was disgusted by their stupidity, and possibly taught them to be smarter.
In "The Main Drain," Plankton is unusually bigger than other episodes.
He and Mr. Krabs is the only in their family to ever make friends with each other, their predecessors are enemies.
In several relatively recent episodes, the inside of his mouth was purple. It was corrected back to red in later episodes.
Early in the series, Plankton is considered the primary villain of the series. Later, as Krabs becomes more dramatically greedy and Plankton becomes less dramatically evil, the role of the main villain of the series becomes more debatable as lots of people think Mr. Krabs is evil.
Plankton is assumed, by many, to be just as old as Mr. Krabs. This is understandable seeing as how they both knew each other since birth, which was noted in "Friend or Foe." However, it is possible that this is ignored in later episodes.
Plankton has inventions for equipment in contrast to Mr. Krabs' spy technology.
As seen in "Evil Spatula," Plankton revealed to have a room full of spatulas in the Chum Bucket.