There’s a reason why ColonelBakarashinIinodevitchZol continues to be the franchise’s definitive monster to this day. After serving as a Nazi officer in World War II, Zol joins Shocker where he gains a reputation for wreaking havoc in the Middle East. He quickly lives up to this reputation when he’s transferred to Japan to deal with Kamen Rider Nigo. He fails to show any sense of shame for his crimes, ranging from brainwashingchildren into becoming Shocker guerilla soldiers to using Wolfsbane to gas attack Goro’s town. Colonel Zol is also a horrible bossto his men. Case in point: Zol praises a revived Egyptus, a mummy kaijin that can incinerate victims, for testing his abilities on (and ultimately killing) one of his mooks. The sequel series Kamen Rider V3 only adds to his crimes. Together with Doctor G, a revived Zol plans to initiate Operation: Japan Annilhilation, which involves unleashing a toxic gas in Hokkaido to kill innocents. Zol also does not care about fellow Shocker and Destron officers at all, as seen when he tries to have fellow Destron officer Ambassador Hell executed for failing to defeat Kamen Rider V3.
N-Daguva-Zeba is the lord of the Gurongi and the Ur-CM of the Heisei era. An Ax-CrazyBlood Knight who absolutely despises the lowly and weak, Daguva doesn’t care about any human or Gurongi lives and is willing to use any means necessary to make humanity as violent and hateful as he. Upon being reawaked from Kuuga’s sarcophagus, he releases the 200 Gurongi and murders the archaeologists, thereby kicking off the series. After his escape, he restarts the Gegeru, a game where Gurongi hunt humans with set rules based on their tribe's social status, and kills 152 of his own kind in Nagano. He then reveals himself to the public by killing Zu-Gooma-Gu for using his armor before resurfacing under the guise of a white-suitedteenagerwith an aura as he unleashes heavy rain in Japan. After Yusuke Godai (Kamen Rider Kuuga) defeats Gadoru, Daguva ambushes Yusuke, mercilessly beats him up, and incinerates numerous people in his wake as he leaves Yusuke behind. After continuing his systematic genocide, he meets Yusuke in Mount Kuro where they have their final fight. There, Daguva finally dies, laughing to the very end hoping that Yusuke would be corrupted by violent hatred.
Years after he blighted television screens in Japan, Go-Jaraji-Da (the Porcupine Gurongi) still stands as the standard to which other kaijin-of-the-week in Kamen Rider are compared to. Jaraji uses his upper-class privileges to choose the 90 teenage boys in Midorikawa High School's 10th grade as his targets for his game. Using super speed and poisonous darts that kills his victims from encephalitis within four days, Jaraji terrorizes and poisons all but one of his targets, condemning many of his victims to slow, brutal deaths and drives others to suicide. As those who commit suicide do not count to his Gegeru, Jaraji compensates by killing high-school boys belonging to other grades and numerous policemen. Most of the other Gurongi are either required to participate in the Gegeru or merely see the Gegeru as a necessary duty. Jaraji, on the other hand, commits his crimes precisely because he enjoys himself watching living beings suffer and coldly admits this to a family before closing in on one of his targets. It's no wonder Yusuke Godai snapped and killed Jarajiso savagely.
Isaka, aka the Peacock Undead, exemplifies how low Manipulative Bastards can go. As the first Category Jack Undead, he designed Rider System 3, a belt that allows the user to transform into Kamen Rider Leangle. Unfortunately, that same belt requires using an improperly sealed Ace card that contains the Spider Undead, meaning that the Undead would mentally enslave its user (as later seen with Mutsuki). After designing the corrupted Rider System, he brainwashed many people that he was going to use as expendable slaves to create his "Ultimate Rider". When this plan failed, Isaka turns his attention to Sakuya Tachibana (Kamen Rider Garren) and attempts to retrieve him as a prototype user. Isaka knows about Tachibana's subconscious fear and takes advantage of it to curbstomp him. Isaka tricks his defeated opponent to getting addicted to Schuld Ketsner seaweed, lying that the aggression-inducing plant would eliminate fear. When Sayoko notices her lover's addiction, Isaka smugly kills her for attempting to clean up her lover. Upon learning about Sayoko's death, Tachibana loses his subconscious fear and eventually gives the bastard exactly what he deserves.
The Lion Fangire, also known as Rook, is an Ax-Crazy, merciless, and easily boredSociopath who treats the lives of humans and monsters alike as a game. Twenty years before Wataru becomes Kamen Rider Kiva, Rook murdered Yuri Aso's mother so traumatically that Yuri swore vengeance on all Fangires (including Wataru's mother Maya). He also was single-handedly responsible for driving the Wolfen race to near-extinction, leaving Jiro as the sole survivor of his genocidal rampage. As the flashbacks progress, Rook devises his personal game to combat boredom called the "Time Play," in which he hunts and eats a select group of people within a time limit. If he succeeds in killing the intended number of people, he rewards himself with ice cream; fail and he self-punishes himself with electric shocks. His already suspect sanity gets even worse when he reawakens and regains his memories in 2008. He proposes a new game which would have him do good deeds before getting himself killed not out of a change of heart but from boredom from constantly playing the "Time Play" game.
The Bat Fangire, more commonly known as the 1986 King, is a ruthless tyrant who fails to understand the concept of love. As the original lord of all Fangires, the King uses his position to annihilate the Merman and Franken races, as well as persecute Jiro (the last Wolfen). When he finds out that his wife Maya has fallen in love with Otoya Kurenai (the original Kamen Rider Ixa), the King offers Jiro, as well as the sole surviving Merman and Franken (Ramon and Riki respectively), a chance to avoid extermination in exchange for killing Otoya. When they choose to escape instead, the King forcibly transforms them into Empathic Weapons. He then kidnaps Otoya and attempts to use his life energy to feed Castle Doran, the King's living castle. When Otoya escapes, the King exposes his lack of any sense of love toward his own wife by using the life of his own son, Taiga Nobori (Kamen Rider Saga), as blackmail to prevent her from seeing Otoya again. This disgusts Kivat-bat the 2nd, who is meant to be the King's loyal Transformation Trinket, so much that he offers Otoya a chance to become Kamen Rider Dark Kiva in order to destroy the King.
The Rhino Fangire was rather nasty. He tricks young people into believing he'll help make their dreams come true to lure them in so he can steal their life force. After killing them, he takes an item from them that relates to their dream as a trophy to put in his "Dream Graveyard". His choice of prey is based solely on a love for crushing the dreams of young people and nothing else. Even Wataru, who had generally tried to find the good in everyone, even Fangires, found his actions unforgivable.
Doctor Shinkuro Isaka, the Weather Dopant, killed Terui's family, modifies Gaia Memories to kill their users so that he can take their power for himself, and is able to use Gaia Memories via direct insertion without any ill effects (typically, repeated use of Gaia Memories via direct insertion warps the user's mind, which shows that Isaka didn't have far to fall). He then tries to get Saeko to kill her own father and take control of the Museum, but winds up getting Hoist by His Own Petard when all of the Gaia Memories he absorbed essentially destroy him from within upon Memory Break.
From W Returns: Eternal, we have Dr. Prospect aka the Eyes Dopant. This man took people from all over the world (their words implying they were kidnapped) to make them into, in his own words, "lab rats" for his Quark Project, giving them psychic powers. The fact that, when he arrives on the scene, every one these people with awesome Psychic Powers is quaking in fear of him shows how horrifically he must have treated them. That is nothing compared to his Heaven's Fall plan. This is a plan so horrible that the previously mentioned Utopia Dopant considered it a brutal act! He would blast the area with an electric pulse, killing anyone that has not lived up to his standards for the project, referring to it as "cleaning out the test pool". When Daido ruins that plan, he reveals that was merciful compared to what happens if they try to escape. The eyes he implanted on them to watch them kill them when they leave his compound. As Katsumi is in shock over the slaughter of the village he'd tried to save, Dr. Prospect is laughing his head off at the fact he'd just slaughtered a village of innocent people. His actions are so horrific that it drives Katsumi insane, a fact that serves as a valid Freudian Excuse for Katsumi's actions in the A-Z movie.
Kazari, the Feline Greeed, is a fine example of how a Magnificent Bastard can also be a Complete Monster. Of the five original Greeed, he has by far the most horrifying way of making Yummy, implanting them in their host and controlling their body like parasites; in some cases, the host is conscious the entire time. In the end, it consumes and traps them inside, fully aware of what is happening. If that weren't bad enough, Kazari's actual actions are much worse. He used Mezool, the Team Mom of the Greeed, and Gamel, a Man Child who really doesn't know better, as lab mice to see what would happen if a Greeed absorbs Core Medals that aren't their own and wasn't the least bit disturbed when this resulted in their mutual demise. In fact, he took advantage of it to assimilate their Cores and get even stronger. After that, he begins raising Lost Ankh as his own personal Tyke Bomb and actively helps Dr. Maki try to destroy the world. He did all this with a sick smile on his face (well, in human form, anyway). He's so evil that even his own kind doesn't care about his demise.
Doctor Kiyoto Maki is a prime example of what happens when antisocial behavior goes off the deep end. Before the day of his abusive sister Hitomi's wedding, Maki burns his sister to death in her sleep just because she was going to abandon him. He then represses these memories and helps a Mad Bomber hosting Mezool's Yummy carry out attacks just to see the Yummy grow, not caring who dies in the process. When the swarm of Yummy hatches, he remorselessly locks his workers inside with them and watches the Yummy slaughter his colleagues. When he teams up with Kazari, his memories of Hitomi resurface, driving him to destroy the world. True to his personal philosophy that "something's true value is only known when it ends", he absorbs five Purple Core Medals to begin transforming into a Greeed himself. Because the core medals make up the essence of a Greeed and give its user Greeed powers, Maki spawns Yummy that are Omnicidal Maniacs, with Maki finding their rampages to be merely "interesting". He also has no sense of loyalty to his allies, as Kazari learned the hard way when Maki impales him and rips all his cores out of him. Near the climax of the series, Maki gives two of his own Cores to Eiji (Kamen Rider OOO) solely to accelerate Eiji's greeedification and tosses the remaining Core Medals from the other Greeed into Uva to forcibly set his ultimate plan of destroying the world into motion. It takes OOO's TaJaDor Combo and Ankh to take out Maki and stop the world's end.
Another Complete Monster is the original OOO. An evil king described as "desire incarnate", his goal was to conquer the world and become an immortal god. To achieve this goal, he had five fully sentient organisms created for the sole purpose of killing them off to reach his goal. He then stabs Ankh, the only Greeed who willingly works for him, in the back for his Core Medals. He's so power obsessed that a living incarnation of human greed calls him Selfish Evil. His own greed ultimately spells his end when he can't handle the power he finally absorbed and it kills him.
Tatsumori Yamada/Aries Zodiarts was transferred around the same time Ryusei came to Amanogawa, and in that amount of time, he's the undisputed king of Subaruboshi high. He forces the whole school (teachers included) in his little play like world where everyone is graded on their performances. If they did bad jobs, he would them into a permanent sleep. He even makes a Deal with the Devil with Meteor, reviving Jiro if Meteor killed Fourze and he follows up on his deal. Then he decides to do a play called "School War" which has the Kamen Rider Club kill students before deciding to reverse the roles and have the Kamen Rider Club being tied up to poles and killed. Thankfully, Gentaro is revived and kicks his ass so badly that he is sent into a coma.
Rem Kannagi, the Big Bad of Movie War Megamax wants to use the power of the Astro Switches and the Core Medals from the future to become an all powerful being known as the Super Galaxy King and will do absolutely anything to accomplish this, and taking a sick glee in rubbing his advantage in the faces of his enemies whenever he gets the chance. He essentially kills Gentaro's girlfriend, Nadeshiko for the SOLU she's composed of, and then rubs that fact in Gentaro's face. He also had no problem killing anyone that gets in his way without an ounce of remorse, or creating clones of all the Greeed and Sonozaki Dopants for his own evil purposes. He gets his in the end though, after being Double Rider Kicked by Fourze Double Rocket States and OOO Super TaToBa Combo, sending him into the path of his own shuttle that runs him over.
Phoenix. While all the other Phantoms (including Medusa) are definitely no saints, Phoenix is a complete psycho who will go to horrific lengths in order to make gates create more phantoms. This is shown quite well in episodes 8 and 9 when he beat a lady just to have a child give into despair. He takes it Up to Eleven in 9 by going the same route as Leo Zodiarts (breaking into the hospital and randomly beating up innocent people, including patients who have no connection to the Victim of the Week at all). Even Medusa is frightened of his tendencies, because he has apparently gone so far as to kill a Gate before the corresponding Phantom can manifest (this is why he is kept to an observatory role at first, rather than being allowed to directly intervene).
Sora/Gremlin may very well count on the fact that as a human, he was a Serial Killer who was responsible for multiple disappearances before he was kidnapped to be made to give into despair. Now normally, one a Human gives into despair and becomes a Phantom they lose almost all aspects of their former personality (take for example Yugo and Misa before they became Phoenix and Medusa). However, it seems Gremlin still has Sora's desire to murder women with long black hair and white dresses. When in Episodes 34-35 it actually seemed like he had noble intentions of protecting the Gate however it was revealed he intended to indulge in his host's former taste, attempting to kill her for the sheer fun of it he also makes no qualms about the fact that the women he murdered he did it for fun or petty revenge.