Shou Tucker

"I don’t see what you’re so upset about. This is how we progress. Human experimentation is a necessary step. I would think a scientist should understand."

- Shou Tucker when confronted by Edward Elric

Early in the Fullmetal Alchemist series, Edward and Alphonse Elric seek information from the "Sewing-Life Alchemist" Shou Tucker who reportedly had created a chimera with the ability to speak. During their time at Tucker's estate, though, the brothers uncover the horrifying truth behind his work.

Manga/Brotherhood
In the original manga and the 2009 series Fullmetal Alchemist: Brotherhood, Shou Tucker is introduced as an alchemist under Roy Mustang's jurisdiction in East City and referred to the Elric brothers due to his expansive work in bio-alchemy. The brothers stay at his estate and befriend his young daughter Nina who referred to Al as "Big Brother" and the family dog Alexander. He mentions that two years ago, his wife left them due to stress from his work, much to Nina's hope that she will one day return. The next day, he created the notable talking chimera that earned him his State Alchemist license-although its words were "I want to die". Tragically, the chimera died not long afterwards, refusing to eat.

Stressed with wanting to keep his license, Tucker goes into his lab and later informs the Elric brothers that he has successfully created another talking chimera. Edward, who has growing suspicions of Tucker's actions in the past, questions about the awfully close timing of the Sewing-Life Alchemist's wife's leaving and the creation of the suicidal chimera, revealing that Tucker had used his own wife to create the chimera. Fears confirmed, Edward angrily reveals the conclusion that Tucker used Nina and Alexander to create this new talking chimera (that refers to Edward as "Big Brother"), an act crossing the Moral Event Horizon. Enraged, Edward brutally beats up Tucker who smugly declares that they are alike in their pursuit of knowledge and alchemical transgressions, likening his use of Nina and Alexander in the chimera creation to the Elrics' attempt to resurrect their dead mother. Alphonse keeps Edward from killing the alchemist and the two have Tucker detained on house arrest.

However, Scar appears on the estate in his personal vengeance to murder all State Alchemists. Killing the guards outside, Scar seizes Tucker's face and kills him with a surge of alchemical energy. Seeing Nina/Alexander chimera as a tortured soul, he euthanizes her.

Tucker briefly appears in a later nightmare of Edward's, accusing him of being a monster for the transgression of attempting to revive their mother. His impression on the brothers is also revisited in the anime, particularly in how Alphonse vows to never let another friend/ally be killed because of them.

2003 Anime
The events of Nina's transformation and its revelation play out in the earlier anime as they do in the manga with some notable changes. Rather than being motivated by his own selfish desire to seek knowledge and reinstate his license, Tucker is pushed to his infamous act by Brigadier Basque Grand who threatens the alchemist with eviction from his estate and an uncertain future for his child if no good results of his research comes up. Instead of being killed by Scar, Tucker is arrested and taken away by MPs along with the Nina/Alexander Chimera. Not wanting her to become a military experiment under Grand's orders, Edward uses alchemy to cause the truck carrying Tucker to crash, freeing the Nina chimera. Despite his efforts, Scar still comes across and euthanizes the chimera, sensing its pain. Tucker is detained and reportedly executed by firing squad.

It is revealed that Tucker is instead made a researcher and test subject in this anime's incarnation of Lab 5. In this time, he created chimeras to be used by the military as weapons and was the only one for the most part that could control them. During this process, Tucker became fused with a canine entity in a kind of reverse crucifixion, becoming a monstrous chimera with alchemically-fused glasses that speaks in a whispered tone. Tucker aids the Homunculi, believing that their nature will provide insight on how to restore Nina back to life. He is shown carrying dolls of his deceased daughter, determined to bring her back and use them as the vessels for her soul. While the 2003 incarnation of Tucker is technically an anti-villain due to his seeking of atonement via reviving his daughter, he is nevertheless willing to cross other lines in order to meet this goal.

After the attack on Lab 5, Tucker joins with the chimeras working for Greed to seek out more information in exchange for acting as a doctor to the chimeras. Following Greed's defeat and the deaths of most of the chimeras, he goes under the service of Frank Archer, still determined to bring his daughter back using the resources permitted by Archer reinstating Tucker's license. When Alphonse has the Philosopher's Stone grafted into his body following the fight between Solf J. Kimblee and Scar, Tucker tricks Alphonse into being used under the pretense of teaching him how to use it. Against everything, Tucker manages to pull off the first non-flawed human transmutation but due to his lack of will, the Nina doll remains in a zombie-like state. He attempts another shot at the process but is halted by Sloth who cruelly points out his failure and takes Alphonse away.

The last time Tucker is seen in the series, he is scribbling down equations on the wall while still trying to uncover the next possible way to revive his daughter.

Trivia

 * Each collection of the manga concludes with a small omake panel showing the characters of note that had died within the contained chapters. Tucker holds the distinction of being shown screaming in Hell as opposed to every other character, including savage characters like Envy and Gluttony, going to Heaven as angels.
 * The event is semi-adapted into the video game Fullmetal Alchemist 2: Curse of the Crimson Elixir in the third chapter "The Tucker Mystery". Tucker himself does not appear in-game, already having been killed by Scar-although the brothers find his glasses and a massive pool of blood. They discover his actions through a diary that, as Edward notes, was "written by someone of an unhealthy mind".
 * He is considered the franchise's most hated character, even more so than the main antagonists Dante and Father.