The Flying Dutchman is a ghost who has a green glow around him, yellow eyes with black irises, a scraggly beard, a pirate hat with a chunk taken out; a handbag marked "Souls," a droopy nose, a coat, little pigtails, and a ghostly tail, and also speaks with a West Country pirate accent. He has a sister named Sally Dutchman.
During all of his appearances, the Flying Dutchman proves to be anything but a "friendly ghost." Though his role in the series is to be the devil of the sea, he constantly varies from a sea demon to a restless soul or even as a psychopompic judge to the dead, the Flying Dutchman has been consistently shown to be gruff, malicious and even downright sadistic, scaring people and stealing their souls out simply for fun, and in his first full appearance, he attempted to steal the souls of everyone in the Krusty Krab simply because SpongeBob's ridiculous costume as the "Flying Dutchman" was the ultimate insult to his image. The latter trait shows that he's extremely prideful.
Despite his antisocial behavior and malevolence, the Flying Dutchman isn't pure evil or without companionship.
He has a number of ghost friends and has the capability to bond with other people in case they have the same interests or objectives (mostly SpongeBob). He is also a notorious womanizer, with not even mortal women being free from his teasers (though the former episode implies that he's divorced). While the Flying Dutchman takes strong delight in scaring people, he doesn't live exclusively to haunt mortals, having sometimes tormented them only out of boredom (scaring SpongeBob for months to wait for his ship to be fully repaired), or otherwise because someone provoked him. Although, he is no saint, the Flying Dutchman has a strong sense of justice and has been known to award people for good deeds done towards him  or to punish wicked souls (taking his role as a Psychopomp very seriously), and has been known to keep promises as seen in "Shanghaied," when he grants three wishes to SpongeBob and the gang in exchange for his sock.
Powers and abilities
The Flying Dutchman is shown to be one of the most powerful supernatural beings in the ocean, rivaling King Neptune. Though The Flying Dutchman's skills vary from episode to episode, he has been consistently capable to levitate, and teleport in a cloud of smoke preceded by a storm. In his first appearance, he is shown to be capable of stealing souls and fire-breathing through his nose. He has also shown to be capable of opening dimensional portals to banish his enemies. He has shown to be capable of manipulating matter (even turning SpongeBob and Patrick into ghosts and making objects appear out of thin air) and granting wishes.
However, of all his incarnations, his most "frightening" appearance was in "Ghost Host," where he was able to shape shift into numerous horrific forms and warped reality effortlessly. Ever since he had been stealing souls and devouring them, there's no approximate limit to how much he can empower himself, and this is what caused him to reach into godhood over the years. The only limitation to his powers regards his ghost tail. Despite being a champion in looping for centuries, he has long forgotten how to tie his shoes and it's later shown that he can't eat without his "dining sock."
His most powerful and dangerous ability, though, was seen in "Ghoul Fools," in which he pulled out one of his eyes and transformed into an atomic bomb, after which he launched himself into the ground. The blast from this attack was so powerful that everyone caught within the blast radius was sent to the Void.
The Flying Dutchman makes appearances in several SpongeBob video games.
The Flying Dutchman has been tricked by Doodle Patrick into thinking that SpongeBob, Squidward, Patrick, and DoodlePants were his enemies. But when Doodle Patrick takes control of his ship, he realizes he's been tricked and relies on DoodlePants to stop him.
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He is named after the legendary ghost ship, The Flying Dutchman, and seems to resemble the famous pirate Blackbeard (Edward Teach) or the ship's captain and mythological character Davey Jones, although according to the legend of the Flying Dutchman the ship's captain is a man by the name of Willem van Der Decken.
The beginning of his theme sounds like the opening of "Duel of the Fates," from Star Wars Episode I: The Phantom Menace.
He doesn't like it when his beard is shaved off because he fears he would get pimples again.
It's also said his beard grows in 1,000 years, but it grew back in several months. His claim could be an exaggeration, though.
In "The Curse of Bikini Bottom," he looks through his closet for a shirt and finds one that is sentimental because he says "It was the shirt I was buried in." However, in "Squidward the Unfriendly Ghost," his origin, from the comic book, says he was never buried and his body was used as a window display so technically, it is impossible for the shirt to be the one he was buried in.
However, he may have indeed been buried eventually, and he remains as a ghost due to having been one for so long.
The Flying Dutchman says he hasn't worn shoes for 5,000 years, so which means that he could be over 5,000 years old. That's older than King Neptune, because he is 5,000 years old.
The Flying Dutchman has to have his Dining Sock on to eat.
In "Shanghaied," it is shown he has a monocle to read
The Flying Dutchman appears to sometimes get emotional, though this very rarely happens.
The Flying Dutchman was absent in both seasons 9 and 10. He returned after a 6-year disappearance in the season 11 Halloween special "The Legend of Boo-Kini Bottom." He would not appear in cartoon form again until "Shopping List" also in season 11.