Fist of the North Star is filled to the brim with villains who prey upon the innocent, from evil warlords to power-mad martial artists. When these bad guys and their minions inflict suffering upon others, it is little wonder that the arrival of Kenshiro is often considered the arrival of a savior — and why it is so satisfying to see him deliver unto these villains what they very much deserve. But even among this bad lot, there are those who qualify as being the very worst of the worst.
Jagi, despite being a comparative wimp to most martial artists makes up for it with his heartlessness and sadism. When he and his brother disciples were trained in the art of Hokuto Shinken, Jagi believed in winning however he could and even attempted to murder Kenshiro when Kenshiro was announced as the successor. Escaping with hideous disfigurement, Jagi became the leader of a roving gang of brigands that murdered families while taking the women to rape and sell into slavery. Jagi manipulated Kenshiro's good friend Shin into betraying Kenshiro, leaving him for dead and kidnapping Kenshiro's love Yuria as well. Among his many brutal murders, Jagi dedicated himself to ruining Kenshiro's good name by impersonating him, and thanks to a serious brother complex he had, when a little boy defended his elder brother, Jagi took the younger brother into the desert, chained him to a cinder block and left him there, solely because "no younger brother should surpass the elder!" He also had a tendency to kill at random if someone's facial features reminded him of Kenshiro and showed a habit of slaughtering his men at the drop of a hat. As Kenshiro said, hell is too good for him.
Amiba, a martial arts prodigy turned Mad Scientist who performed hideous experiments on innocent people. Having townspeople brought to him, Amiba would experiment by pushing their pressure points in ways that would inflict hideous agony or even bring lingering death, or just make their limbs or bodies explode. Amiba showed no hesitation performing these experiments on children and impersonate Kenshiro's elder brother disciple Toki in these actions. Amiba did so in order to ruin Toki's name, knowing Toki was a kind man who dedicated his life and talents to helping others. The reason for his hatred? Amiba's ego couldn't stand Toki receiving praise for his healing abilities and when Amiba carelessly injured an old man to show he was better, Toki accidentally struck Amiba out of the way to save his victim. Amiba is willing to kill countless people, inflicting emotional and physical trauma on everyone he encounters solely to satisfy his own ego as a 'genius'
Emperor Souther, the Holy Emperor, in the OVA has all of the evil deeds of his manga counterpart, but none of the Freudian Excuse. Souther runs a brutal empire that enslaves thousands of innocent children and works them to death. He poisons supplies he knows the rebellion will steal (and knows they'll give the food to their children first and throws himself huge banquets, eats a small plate, and destroys the rest, all for the sick glee of watching the starving slaves suffer, while having them beaten if they try to eat any of the excess. His old friend Shu, the rebellion's leader? Souther forces him, with cut tendons, to make his way up an enormous pyramid holding the enormous stone cap piece meant to finish it...if he drops it, every single slave will die; and if anyone helps him, Souther tells them their families will be executed. And then, once Shu finally does make it to the top of that pyramid? The bastard orders his archers to put arrows into him, and then finishes him off with a thrown spear.
Jackal, the bandit lord that Kenshiro takes on after the business with Shin, somehow manages to rival even the above three in depravity. Jackal and his men are harassing a village with an orphanage for its water. Jackal's men murder seven-year-old Taki for trying to collect the water they claim as "theirs", even if without the water, the rest of the orphans and their caretaker Toyo will die of thirst. But even after the orphans and Toyo are subdued, Jackal feels the need to sadistically kill them. Jackal purposefully gives Toyo a mortal stab wound, just so she could live long enough to watch one of the orphans hanged by his men. To make matters worse, Jackal then tries to kill the kids by strapping dynamite to their backs in order to keep Kenshiro from going after him. It's not only his enemies who should fear Jackal, either. He's a ludicrously Bad Boss, killing his own men for the slightest provocation and sacrificing his trusted lieutenant just to slow the vengeful Kenshiro down, and is eventually forced to slaughter his whole gang when they rebel against his mistreatment. When Kenshiro tracks him down at Villainy Prison, Jackal manipulates a giant Psychopathic Manchild convict by the name of the Devil's Rebirth to become his pawn to fight Kenshiro by pretending to be his long-lost brother... and when the Devil's Rebirth fails, he thanks Kenshiro for rescuing him from the 'evil monster' that had 'captured' him, and encourages him to kill him quickly.
Uighur is the sadistic warden of the prison-city Cassandra, dumping ground for the warlord Raoh's few living enemies. Cassandra is nicknamed the 'City of Wailing Demons' due to the unimaginable hardships its inmates endure, hardships that Uighur is so delighted by that he alters prisoner treatments to get just the right pitch and timbre of lamentation. He is extremely proud of his prison's reputation as The Alcatraz, stating that "the legend of Cassandra is my legend as well", and maintains its zero-escape record by gruesomely killing any prisoners who try to escape, as well as anyone from outside who tries to break them out (the latter along with a cell of randomly-selected prisoners, just to make a point). His own staff fare little better - for example, his gate guards, Raiga and Fuuga, are kept in line by the threat that if they disobey him, their younger brother will be pecked to death by Uighur's pet eagle. The only people he tries to avoid killing are those willing to die, because that spoils half the fun, and he'd much prefer to instil the appropriate fear of death in them before murdering them really horribly.
Jakoh, Evil Chancellor of the Celestial Empire, was never a nice person, waxing gleefully enthusiastic about infanticide when the Empire turned out to have one heir too many, but when Raoh came to their village, sensed his evil, and advised the man's adoptive brother Falco to kill him on the spot to avert future suffering, few knew how right he would be. After Raoh's death created an Evil Power Vacuum, Jakoh moved to fill it, using the young Celestial Emperor Rui as a Puppet King and manipulating Falco, her oath-sworn bodyguard, into doing his dirty work by using her as a hostage, keeping her in such unpleasant conditions that she eventually went blind. The Celestial Empire was exceptionally repressive, rewarding the wealthy and brutalising the poor whilst punishing dissent with death so liberally that the concentration camps overflowed and malcontents were executed in the streets. Eventually, Jakoh's paranoia led him to endorse outright genocide, ordering the reluctant Falco to obliterate the nations formed under the Hokuto Shinken and Nanto Seiken martial art schools and beating him when he failed. His hatred of Hokuto was not the only legacy of his encounter with Raoh - Jakoh had an intense fear of the dark. As a result of this, he would lapse into murderous tantrums when the lights dimmed too much, and worked thousands of slaves, old and young alike, to death in keeping the capital of the Celestial Empire brightly-lit. Throughout it all, he never showed any remorse or regret for his actions, instead taking sadistic delight in Falco's disgust and horror at the latest atrocity he would force him to perform.