Complete Monster/One Piece

While many of the baddies from One Piece, like Don Krieg, Arlong, Crocodile, Enel, and Blackbeard walk the range from insensitive jerks to all out line-crossing assholes, there are a few villains who believe that the above characters just weren't evil enough:


 * While the first couple of One Piece villains were simply obnoxious assholes whose most heinous deeds were committed when provoked, early villain Captain Kuro was the first of many true monsters in the franchise. While first appearing as the snooty but well meaning butler serving a kind-hearted woman named Kaya, Kuro was secretly a retired pirate captain who had grown sick of running from the law and was hatching a plan to raze the island he was hiding out on to the ground in order to obtain a large sum of money, most of it from Kaya's inheritance. He had his old crew of Black Cat pirates hiding in wait ready to invade the town and assault it while Kuro would attempt to hypnotize Kaya to leave him as the one to inherit her large sum of money before executing her. He didn't even NEED to kill Kaya, but he wanted to in order to have peace of mind, since he had always hated Kaya and thought catering to her whims to be degrading. Since he'd been acting as a father figure and friend to Kaya for years, this is truly despicable and heartless, and incredibly hurtful to Kaya when she gets told it by the man himself. The kicker? He also attempted to wipe out his own crew in order to keep up the charade of Kuro dying a long time ago, showing that he was enough of a scumbag to view his own allies as disposable pawns, a view which seriously pissed off Monkey D. Luffy who holds camaraderie and friendship in high regard. It's hilariously fitting that Kuro's fate after the subsequent beat-down by Luffy was to end up forced back into the role of a pirate captain, on the run for the rest of his life with Marines and bounty hunters in hot pursuit.
 * The method Kuro used in order to fake his death before taking on the Klahadore persona already showed how little he valued his crew member's lives: he had his first mate Jango hypnotize a crewmate of theirs in order to brainwash him into believing that he was Captain Kuro and left him to be executed so Kuro could save his own skin. While Alvida, Morgan, and to an extent Buggy were quite dickish to their henchmen (Morgan executing a marine who wouldn't kill a small child being the worst of the bunch), Kuro is the kind of guy who will happily slaughter you even if you are a loyal pirate as long as it would benefit him.
 * Spandam was the first villain in the series to show that even slimy, cowardly weaklings were more than capable of being capable of incredible evil. While he at first seems like a clumsy, comedic villain in the vein of characters such as Buggy the Clown, he quickly shows that he's a complete bastard. While he follows the doctrine of Absolute Justice, he's more interested in aquiring weapons and stroking his ego as opposed to altruistic reasons and isn't afraid to backstab, exploit loopholes, or exploit others to get what he wants. In the past, he destroyed a judiciary ship and blamed the warships Franky's mentor Tom created, and carted him off to Impel Down, which is an incredibly hellish and brutal prison. During this event, he caused Franky's body to be nearly mangled beyond repair by running him over with a train, cackling the whole time. If that wasn't bad enough, there's also his treatment of the captive Nico Robin. He spends most of his time ruthlessly beating her, tossing her down flights of stairs, and psychologically tormenting her as a means to completely break her spirit. And on top of that, he attempts to blame his group of incredibly powerful assassins for his shortcomings, and tries to have them executed (This backfires however). Needless to say, it's incredibly satisfying to watch Robin slap him silly in return and break his spine, leaving him as a cripple with a pack of pissed-off powerful assassins on his tail.
 * The Celestial Dragons (Save for Donquixote Doflamingo so far, though he's hardly a saint himself) are slave-owning arrogant bastards. They are nobles who are descendants of the World Government's founders that have tons of political power due to their lineage, and gleefully abuse it with reckless abandon knowing full well that the "commoners" can't fight back without being executed by an Admiral for it. When a slave tries to escape and blows up his collar, St. Charlia of the Celestial Dragons shoots him while complaining about how pathetic it was that he was whining about his family (who he just wanted to see again). Her brother, St. Charloss (introduced while riding on a slave), enraged that a doctor and a nurse carrying a wounded man would dare not to kneel in front of him, kicks the injured man off of the stretcher. He then decides to take the nurse as his wife. When her fiancee complains, he shoots him. In fact, he attempts to shoot anyone who irritates him with full legal immunity for himself, and treats anyone lower on the social ladder as less than dirt, even beating a wounded man for not kneeling to him. He and his family also attend a slave house where they purchase slaves for any purpose they want, and when the reformed villain Hacchan encounters Charloss, Charloss shows himself as a murderous racist towards the Fishmen and nearly kills Hacchan by gunning him down. And if that wasn't enough, he tried to buy a mermaid named Kamie for the sole purpose of feeding her to his pet piranhas. Needless to say, they are among the most loathed characters in the entire series in and out of the One Piece universe for a very good reason.
 * As Charloss shows, World Nobles pretty much hold Fishmen in high contempt, even moreso than their usual human slaves. One notable example is St. Mjosgard, a Celestial Dragon who got cocky enough to infiltrate Fishman Island in order to reclaim a few escaped slaves. Whenever the local Fishmen decided to lynch him and write off his death as a shipwreck, Queen Otohime decided to take the bullet for him and saved his life. He repaid her... by trying to shoot her for her trouble.
 * Shiliew/Shiryu of the Rain, former Head Jailer of Impel Down counts. Completely Ax Crazy, he murders dozens, if not hundreds of prisoners for fun, claiming them to be "just trash" and making the actual Head Jailer Magellan completely disgusted.  It's pretty clear he has no empathy and loyalty for anyone but himself.
 * Admiral Akainu, a wonderful example of a Knight Templar who crosses the barrier between Well-Intentioned Extremist and Complete Monster. He debuts while crossing the Moral Event Horizon: he orders his subordinates to blow up a ship of evacuees that the Marines had promised to spare. His justification was that he thought that if there were any survivors from Ohara that the world would be in grave danger, although there's no proof that survivors of Ohara actually present any danger. Later in life, he brutally murders anyone who tries to flee from the battle at Marineford. Then there's what he does to  He moves the series into Darker and Edgier territory by causing the first major present-day story death. Let's put it this way: when Sengoku stepped down and Aokiji had to fight Akainu for the position, which Aokiji ultimately lost, he left the Marines rather than serve under him. The guy is that bad.
 * There is also Hody Jones, a Fishman who takes Arlong's Fantastic Racism and turns it Up to Eleven. He's more brutal, more racist, more treacherous, and more cruel, but the kicker? He pulls a reversal on Arlong's sole Pet the Dog moment; whereas Arlong was mortified when Luffy used a Fishman as a human shield, Hodi actually uses a Fishman as a human shield against an attack. One of Arlong's former crew, Hatchi, stated that, while Arlong was a bastard through and through, he'd never hurt a Fishman no matter what. Hody, on the other hand, is known for killing any who talk to or know them.
 * Arlong himself is this if you don't see his care for his Fishman crew's well being to be redeeming enough, as he seems to lack any personal relationships, valuing his crew mates for what they are instead. Everything else about him is just vile. To wit, Arlong is a sadistic Fishman pirate who invaded Nami's hometown and quickly began to extort money from the villagers, ordering them to pay a large sum of money or to forfeit their lives. Unfortunately for Nami and her sister Nojiko, their mother (Adoptive in Nami's case) Bellemere didn't have enough money to pay for all three of them, and instead chose to pay for them while sacrificing herself in their place. After taking sadistic pleasure in snuffing out their mother's life and using her as an example to humans who defied him, Arlong immediately captured Nami and decided to use her as his personal map-maker, offering to let her go free if she put her life on the line to deliver them a total of 100,000,000 berries (Currency in the One Piece universe). However, Arlong had no such plans to let her go; he arranged with a corrupt Marine official to confiscate her money so she could serve Arlong forever as he found her map-making talents far too useful for her to be let go. What's worse is that he still considered Nami to be his shipmate, infuriating Luffy with how his actions show that he doesn't truly know the meaning of the term. It doesn't need to be said that it's damn satisfying to watch Luffy pummel the living hell out of him and free the oppressed humans from his tyrannical rule. He was so bad that prior to a Retcon in later chapters, Arlong actually appeared to have been Killed Off for Real at the end of the fight.
 * Punk Hazard gives us the truly detestable Mad Scientist Caesar Clown. A Villain with Good Publicity who's convinced people he's a kind master and scientist who just wants to help people. The truth is that Caesar is violently jealous of his former associate Dr. Vegapunk and once took that frustration out by blowing up an island. In the present, Caesar keeps multiple children in his lab with promises to cure them of their sickness, and gives them candy to help them. The 'candy' is in truth an addictive drug to keep them enslaved to him, and his experiments will cause their deaths in five years. He shows no remorse, laughing he can always get more children. Caesar also saved pirates and sailors from death, but uses them as test subjects as well and turns them against their captain who was just trying to save them from Caesar. When his back is against the wall, Caesar has no compunction killing these men with a poison gas he unleashes in an attempt to kill Luffy. Caesar has no loyalty to anyone but himself and his psychotic ego and combines scientific drive with a sadist's streak a mile long.