Complete Monster/Fullmetal Alchemist

Fullmetal Alchemist has many evil villains, but a few stand out as particularly horrible.
 * The manga and second anime series, Brotherhood, has some surefire examples:
 * There's Shou Tucker, a Mad Scientist who transforms his own daughter into a Half-Human Hybrid, partly to see if he can and partly to retain his State Alchemist status. He had previously done the same thing to his wife. He's the only character who even comes close to triggering Al's Berserk Button, and what he did leaves a stain on the Elric brothers' memories for the rest of their lives.
 * Just to put things in perspective: of all the characters who died in the story (shortly after Tucker's arrest, Anti-Hero Scar breaks into his house and bloodily murders him), he's the only one who was sent to Hell in the "In Memoriam" omakes. The authoress Hiromu Arakawa allowed even characters like Envy or Kimblee to get to Heaven, because she thought there was still something worth saving about them. With Shou Tucker, she was absolutely merciless, and with good reason.
 * Even after he's died, it gets even worse. Later on, it turns out that what he did was totally and completely pointless because the military already had much better chimeras. Imagine straight up humans who can harness the instincts of a specific animal and even turn into that animal temporarily in order to fight better, like the Lizard with none of the Super-Powered Evil Side effects. Compare that to the paralyzed husks of pain that became the Tucker family.
 * The Big Bad, Father, is often seen as one,
 * Zolf J. Kimbley is an odd example. On the one hand, he's a Sociopathic Soldier who sees killing as a job, Loves the Sound of Screaming, and enjoys demolishing entire city blocks with his explosions. He sees no moral difference between saving lives as a doctor and taking them as a soldier and is willing to side with the homunculi just to see how the conflict is going to turn out. On the other hand, he's also deeply self-aware of his own psychopathy, loathes hypocrisy, and is a major believer in human potential. Kimblee essentially straddles the line between CM and Even Evil Has Standards--he does have a code of conduct and a sense of right and wrong, but it's a code that no human being would ever see as moral.
 * The unnamed and utterly heinous Dr. Goldtooth is essentially Tucker 2.0.
 * From the Brotherhood movie, we have Security Chief Atlas, who killed the movie's female protagonist's parents, . He also stabbed the guy who was secretly in on this as well because he needed more sacrificial blood. He gets his comeuppance when a  Julia and   kill him in the end.
 * The 2003 anime version has its own set of monsters:
 * Mugear wanted to introduce a toxic chemical into pregnant women to produce an alchemical amplifier. Before that, he had no problems producing said amplifier at the cost of the villagers' health. He also murdered Nash Tringham, the inventor of the method, after he refused to use the method or continue the research on it due to the health risks for the people of his village and tried to sabotage its use by Mugear.
 * Brigadier General Basque Grand (a Reasonable Authority Figure in the manga) is portrayed as a sadistic Colonel Kilgore and one of the key players in the Ishbalan massacre, who laughed maniacally as he gunned scores of civilians down with his Philosopher's Stone, authorizing its use in order to turn the massacre into a massacre. Grand When he discovers what Shou Tucker had done to his daughter, he decides to cart her away for study, presumably so he could bully Tucker into making more chimeras lest he lose his State Alchemist license. When Scar blows his brains out, it is very, very satisfying.
 * The Big Bad,, is an obvious one. She manipulates and abuses her homunculi servants and sends them to their deaths if they don't do exactly what she wants. Their desire to become human leads them to question if she really intends to make them human (she doesn't), and she can't have that. She plots the destruction of an entire nation in the hopes that it will convince someone to create a Philosopher's Stone, which she can then steal in order to live a few years longer (when she's already Really Seven Hundred Years Old). And that's on top of already being a body-snatching bitch who plans to hijack the body of Rose, who already went through serious Break the Cutie, including.
 * Then there's The Big Bad's Co-Dragons, Pride, who willingly oversees the destruction of his own nation and strangles his own son to death, and Envy, a Shapeshifting psychopath whose Freudian Excuse (Parental Abandonment ) doesn't even come close to making his raging sadism, brutality, and contempt tolerable; he gets his jollies out of murder, kills the comic relief while in the form of his wife, and elevates Kick the Dog to an art form, before finally.
 * Last but not least, we have two characters who are very different from their original incarnations:
 * Zolf J. Kimbley: Unlike his manga counterpart, who has a definite case of Moral Sociopathy going on and believes Rousseau Was Right, this version is a Psycho for Hire, Nietzsche Wannabe, and Misanthrope Supreme par excellence, who Loves the Sound of Screaming and isn't afraid to share it with you. He committed genocide in Ishbal, tortured Scar by blasting him apart one piece at a time, blew up his fellow prisoners in order to escape from prison, betrayed Greed to Frank Archer, tries to murder Al soon after his reinstatement, reenacts the Ishbal genocide in Liore, and finally dies while trying to take Al and Scar with him, succeeding in killing Scar. A truly appalling mix of rage, hatred, and pure nihilism.
 * Barry The Chopper: Unlike his manga incarnation, who was Played for Laughs, his iteration in the 2003 anime was far more vicious and horrifying. Barry was once a simple butcher living in Central City who had grown bored with his life of cutting up pigs and cows. One day, to see what it felt like, Barry decided to chop up his wife and quickly found that he loved the sensation. What followed was a string of women being brutally murdered. Barry's killing spree came to a temporary halt when he was arrested after trying to kill the Elrics' childhood friend, Winry. Rather than be executed, Barry was experimented on, had his soul bound to a suit of armor, and became one of the guards for the Fifth Laboratory. After the lab's destruction, Barry slaked his bloodlust by joining a group of mercenaries to slaughter a camp of harmless Ishvalans. An utter sociopath, Barry killed people for no other reason than because he enjoyed it. When asked by Alphonse if Barry was afraid that he wasn't the real Barry and was just an artificially constructed soul, like Barry accused Alphonse of being, Barry stated that it didn't matter if he was the original Barry or not* . Barry claimed that so long as he had the ability to kill people, he loved who he was: "I kill therefore I am."
 * Barry The Chopper: Unlike his manga incarnation, who was Played for Laughs, his iteration in the 2003 anime was far more vicious and horrifying. Barry was once a simple butcher living in Central City who had grown bored with his life of cutting up pigs and cows. One day, to see what it felt like, Barry decided to chop up his wife and quickly found that he loved the sensation. What followed was a string of women being brutally murdered. Barry's killing spree came to a temporary halt when he was arrested after trying to kill the Elrics' childhood friend, Winry. Rather than be executed, Barry was experimented on, had his soul bound to a suit of armor, and became one of the guards for the Fifth Laboratory. After the lab's destruction, Barry slaked his bloodlust by joining a group of mercenaries to slaughter a camp of harmless Ishvalans. An utter sociopath, Barry killed people for no other reason than because he enjoyed it. When asked by Alphonse if Barry was afraid that he wasn't the real Barry and was just an artificially constructed soul, like Barry accused Alphonse of being, Barry stated that it didn't matter if he was the original Barry or not* . Barry claimed that so long as he had the ability to kill people, he loved who he was: "I kill therefore I am."