The various Gundam series have a habit of trying to show war in various shades of gray, and as a result, most villains (if they can even be called that) are tempered with sympathetic human qualities. However, there are still exceptions to the rule...
The Titans from Mobile Suit Zeta Gundam were a haven for terrible people of all kinds, but none quite as bad as these two:
YazanGable, a thuggishPsycho for Hire known for his Catch Phrase: "Iím gonna violate you!", is an adrenaline junkie who freely admits that the whole reason he joined the Titans was so that he could satisfy his bloodlust by legally killing members of the Anti Earth Union Group (AEUG). He has no interest in the rules of warfare, murders solely because he is good at it, and gladly participates in the Grenada Colony Drop, which would have killed thousands of civilians, seeing it as an opportunity to shoot down anyone who tries to defend Grenada. When his superior officer, Jamaican Danigan, tries to stop Yazan from fighting a pointless battle, Yazan arranges for Jamaican and several members of the Alexandria's bridge crew to die at the hands of AEUG ace Emma Sheen. He later betrays Titans' leaders Jamitov Hymem and Bask Om to PaptimusScirocco because he believes that Scirocco is stronger than they are, and in the finale goes on an epic killing spree that results in the deaths of Katz Kobayashi, Henken Bekkener, the entire crew of the Radish, Emma Sheen and his own teammate Reccoa Londe whom he kills alongside Emma. He's consistently characterised as a feral predator rather than human being, and it's worth noting that a) he was likely the inspiration for Rakan Dahkaran, Ali Al-Saachez and Decil Galette, three of the other characters on this list, and b) does all of this while being a Badass Normal in a show full of people with Psychic Powers, getting by on sheer force of evil.
While the anime version of Glemmy Toto had enough redeeming traits to keep him off this list, the same cannot be said for his manga counterpart, a vicious Smug Snake and Starscream who is bad news from his first appearance to his last. Coldly manipulating Puru, an unstable child soldier into doing his killing for him, Glemmy keeps a small army of brainwashed clones of her as backup for when she inevitably dies on him. He burns down an entire village to draw out protagonist Judau Ashta, has a defecting Puru killed by her Evil Twin Puru-2, and eventually betrays Big Bad Haman Khan, triggering a devastating Enemy Civil War in the process, as he aims to make himself the dictatorial ruler of both Earth and the colonies, unleashing his entire clone army in the process. Idolising the franchises' original CM, Gihren Zabi, Glemmy promises to be every bit as brutal a tyrant as he was, and betrays no concern at all for the dozens of little girls who are dying to make his dream a reality.
The original show, in the meantime, has Axis-Zeon Ace PilotRakanDahkaran. An expy of Zeta's Yazan Gable, Rakan is, like his inspiration, a brutal, nigh-unkillableBlood Knight with a tenuous grasp of personal loyalty, albeit with some actual command talent thrown in. Cold-blooded and willing to do whatever it takes to get the job done, Rakan has no qualms about harming civilians. This is best demonstrated in Episode 35, where he impassivelyguns down hospital ships and evacuation craft fleeing the Dublin Colony Drop, and destroys roads and bridges in order to make sure that nobody escapes the blast radius. He kills longtime Gundam veteran Hayato Kobayashi when the latter tries to stop him, and following his defection from Haman's forces willingly kills many of his old comrades, including Anti-Villain Mashmyre Cello and Royal Guardsman, Lance before being stopped by Judau. Axis' go-to guy for the dirtiest of jobs, Rakan proves that in the end, his only loyalty is to himself.
Mobile Suit Victory Gundam has Fonse Kagatie. The Prime Minister of the Zanscare Empire, he cynically exploited the messianicpsychic Maria Armonia's harmless pacifist cult to create a brutal military dictatorship, with Maria as his powerless figurehead. Whilst, as the de facto ruler of Zanscare, he was responsible for green-lighting all of its atrocities (which included the mass execution of dissidents by guillotine, burning entire towns to flush out the League Militaire, and genocide by giant motorbike), his worst act by far was creating and deploying the Angel Halo. The Final Solution to Zanscare's war with the Earth Federation, the Halo was a psychic Doomsday Device designed to wipe out all intelligent life on Earth via Mind Rape, allowing Kagatie's empire to move in and take the planet unopposed. For extra evil points, its power source was Maria (later replaced by her eleven-year-old daughter) and thousands of her followers, who he tricked into believing that they were broadcasting messages of peace and goodwill rather than orchestrating a total planetary genocide. This also meant that they served as Human Shields for the Halo, ensuring that every bit of damage it took was measured in innocent lives.
Mobile Suit Gundam Wing is perhaps the lightest of the series, with most of the villains being Well Intentioned Extremists, being too pathetic to qualify, or being out and out antivillains. None of those things can be said about the Romefeller Foundation's Chief Engineer, KenTsubarov. A loud, abrasive jerkass, with No Indoor Voice and a Hair-Trigger Temper, Tsubarov eventually reveals himself as a Blood Knight by proxy who enjoys watching his Mobile Dolls slaughter enemy soldiers a tad more than is healthy, supporting Disc One Final Boss Duke Dermail in the hopes that the latter will trigger an enormous war for his Dolls to show off their skills in. When Lady Une, a major supporter of his project, reveals that she likes the automated Mobile Dolls because they will cut down on human casualties, Tsubarov turns on her—he wants his Dolls to have the chance to kill people, and plenty of them. When the White Fang rebellion reaches the colonies, Tsubarov betrays Une, seizing control of the colonies, attempting to murder the captive Gundam pilots by cutting off their oxygen, and gunning Une down when she tries to interfere. He proceeds to improve his Dolls, and begins construction of the Kill Sat/BattlestarLibra for his boss. When the rebels come for him, Tsubarov finally snaps, undergoes a huge Villainous Breakdown, and turns his Dolls loose on the civillian population, ranting like a madman the entire time about how, through them, he will achieve invincibility.
The Spin-Off novel Gundam Wing G Unit brings us Dr. Berg, a Mad Scientist suffering from a terminal case of Chronic Backstabbing Disorder who is willing to betray and murder in order to complete his research and create the most powerful Gundams ever, as he takes pride and joy in inventing newer and newer ways for humans to kill each other. He has no regard at all for human lives and only considers people as guinea pigs for him to toy with. It is also revealed later on that he arranged for the death of Dr. Burnett and his wife, the parents of series protagonists Odin and Odel, in order to divert fundings from their research to his own weapon manufacturing...and the reveal sends Odel, who is normally quite The Stoic, into an Unstoppable Rage and drives him to kill Berg. Unfortunately, the mad doc initiates a Suicidal Cosmic Temper Tantrum and activates his Grand Shirio's doomsday program to destroy the colonies and drop itself on Earth to pollute it with its nuclear engines.
After War Gundam X gives us Seidel Rasso, leader of the Space Revolutionary Army. In the aftermath of a war that nearly wiped out humanity, Rasso became the leader of the twelve million people living on the colony of Cloud 9. Turning it into a Police State, Rasso suppressed all dissent, and preached a Master Race philosophy, founded on the notion that since Newtypes could only be born in space, the colonists, rather than the people of Earth, should control the destiny of the human race. Knowing this to be false, Rasso also kept all information about Newtypes on Earth quiet, while gearing up for another war. Destroying the rebellious colony of Satelicon, including its largely civilian population, with photon torpedoes in order to consolidate his power, Rasso had his right-hand man, Nichola, arrested and summarily executed for suggesting peace talks with the New Earth Federation, and tried to use a Kill Sat to exterminate those humans remaining on Earth. When the supercomputer DOME revealed that Newtypes were really no different from the rest of humanity, Rasso refused to accept it, even as his archenemy (and ardent Newtype hater) Fixx Bloodman of the NEF reconsidered his own position. Pushing his own lies to the end, Rasso's last act was to violate a ceasefire between himself and Bloodman, ranting about how Oldtypes like the NEF president were all scum who deserved to die.
Gym Ghingnham of ∀ Gundam is many things, none of them pleasant. He's a cunning and ruthless manipulator with an intuitive grasp of Obfuscating Stupidity, a brutal warlord whose spurious 'warrior philosophy' is chiefly an excuse for hurting people and can be dropped at a moment's notice if it gets him into trouble, and an entitled Psychopathic Manchild who sees war as a game and human lives as points on the scoreboard. He threatens to rape his guest/prisoner Kihel Heim, casually murders his subordinates on the slightest pretext (up to and including an impromptu weapons test for his new suit), and attempts to restart the Dark History, the centuries of apocalyptic warfare that nearly brought about the extinction of humanity, because he thinks it'd be fun. His crowning moment of evil likely comes when he kills his own Dragon for offering him assistance in a battle...only to then turn around and beg for help from another subordinate the moment the fight is going against him.
Ali Al-Saachez exists solely to make the world a much worse place. A self-admitted Psycho for Hire who flat out states that he's "the worst kind of person there is," Ali will do anything if the pay is right. He raised an army of Child Soldiers while in Krugis, convincing them that every act of terrorism they committed, (including murdering their own parents) was being done in the name of God—a God that Ali does not believe in; he was in it for the money. During the course of the show he proceeds to kill off a sizeable number of characters, including Lockon I, supposed allies Michael and Johan Trinity, and Kinue Crossroad, singlehandedly burn down a country, and aid an Ancient Conspiracy in a successful bid to Take Over the World. He even goes out a bastard, dying while trying to backstab a man who had just sparedhis life. Ali is inordinately proud of his worst acts and brags about them whenever he has a captive audience ("See that kid? Somebody kidnapped him, raped his mind, and turned him into a child soldier." That someone, was me!"); it says a lot about his character that he actually finds empathy disgusting.
Ali's boss, Ribbons Almark, is just as bad. An unbelievably arrogant Artifical Human, Ribbons views himself, and his fellow "Innovators" as a Superior Species destined to rule over humanity. Setting himself up as a messianic figure (while harbouring even greater delusions of grandeur), Ribbons takes control of the United Earth Federation after betraying Alejandro Corner (who genuinely liked him) and arranging for the death of Aeolia Schenburg, his creator. Almost all of the above-mentionted atrocities that Ali Al-Saachez commits—razing Azadistan, murdering the Trinity siblings (whom Ribbons genegeneered in the first place), attempting to kill all the members of Celestial Being—were done on Ribbons' orders, and once he's ruler of the world, he really comes into his own, ruthlessly manipulating Louise Halevy (a horribly unstable Dark Action Girl) into becoming his pawn, forcing Manchurian Agent Anew Returner into a battle to the death with her Love Interest, using the A-Laws to crush anyone who gets in his way, and utilising a Kill Sat to murder thousands of people. Why does he do this? Because it's his way of stroking his own inflated ego. In general he's less a character and more the superiority complex that walks like a man.
Decil Galette of Mobile Suit Gundam AGE is what happens when you take the Enfante Terrible trope and turn it Up to Eleven. A seven-year oldSociopathic Soldier and Vagan Ace Pilot when first introduced, Decil sees war as a game, and his victims as nothing more than expendable toys. As the pilot of the Zedas, he spearheads genocidal attacks on colonies, and is implied to be the one who orphaned Yurin LíCiel. He subsequently hijacks the AGE-1, and tests out its capabilities by butchering his own allies. He later captures Yurin, puts her inside of a remote-controlled mobile suit, and forces her to attack her Love Interest, Flit. When Yurin tries to fight off his control, Decil kills her, while laughing about how she was ďjust a plaything.Ē Thatís all in the First Generation. By the Second Generation, heís thirty-three years old and has, if anything, gotten worse. Deeply resentful of his younger brother Zeheart for being promoted past him, he takes more and more insane risks. This ultimately leads to his getting most of the Magicians Eight killed as a part of a grudge match against Flit and murdering Flit's friend, and Flit's son Asemu's mentor, Woolf. It gets to the point where Zeheart, realizing what his brother has become, leaves Decil to die at Asemuís hands in the aftermath of a losing battle.