Scar's brother

Scar's brother (real name unknown) was an Ishvalan scholar who studied Alchemy and, in the manga and the 2009 anime, Alkahestry.

He is responsible for saving his brother's life during the war in Ishval, sacrificing himself and giving away his right arm, which later allows Scar to kill state alchemists. He is never seen in the present time as he died during the Ishval Massacre, but he is seen in several flashbacks. Like his brother, his name has never been revealed.

Personality
A kind man and an excellent scholar, he was enthralled with learning about alchemy and later alkahestry. He was almost always seen reading books and writing notes, and was quite diligent in his studies. His intelligence was so great he was able to learn and discover the unnatural flow of alchemy in Amestris and develop a reverse transmutation circle to fix it, an amazing feat considering he had never been to Amestris or known of the homunculi. His notes were extremely hard to decipher as well, with even Dr. Marcoh having trouble and it took a chance accident to realize the hidden meaning behind his notes. He once told his brother Scar that Scar would make a better monk than him because he was a better fighter and Scar's brother never liked fighting, implying he was a pacifist. He also loved his brother dearly, evident by the fact that he sacrificed himself to shield Scar and gave Scar his right arm.

Manga and 2009 Anime
Scar's Brother first appears in Chapter 58: The Footsteps of Ruin, researching Amestrian and Xingese Alchemy in the hopes that he will be able to help in the fight against the state alchemists. He is the first to discover that something is strange about Amestris' alchemy. During this time, he tattoos both of his arms with a strange combination of Xingese Alkahestry and Amestrian Alchemy; the left being primarily reconstruction, and the right, deconstruction. Before the state alchemist Solf J. Kimblee arrives, he gives his research notes to his brother (who later comes to be known as Scar) for safe keeping, saying that a warrior priest is more likely to survive than a book worm. He shields Scar from the explosion resulting from Kimblee's attack, then gives Scar his right arm in order to save his life, and subsequently dies.

Scar goes on to hide his brother's research notes in a small cabin near Briggs. His notes are what reveal to the main characters what the modified country-wide human transmutation circle looks like, as well as the Alkahestric Reverse.

2003 Anime
In the 2003 Fullmetal Alchemist anime, Scar's older brother attempted human transmutation in order to revive the woman whom both he and his brother loved. The transmutation failed, leading to the birth of the homunculus Lust.

It is unclear what Scar's brother sacrificed for the transmutation, due to his apparently complete body, but if one assumes that the blood seen on his clothes immediately after the transmutation is his own, it is possible that he lost either some of his internal organs or his genitalia, which could be connected to the 'love' part of the transmutation (this is the only known attempt to resurrect a lover, rather than a family member). A white "scar" can be seen around this general area during a flashback of the Ishval massacre.

Shortly after his failed transmutation, he was exiled by his people since alchemy was considered taboo and against the teachings of Ishvala. When the Ishval Civil War occurred, he returned to offer his knowledge of Philosopher's Stone to end the war. The people of Ishval had no choice but to accept the help of an outcast. When he found out that the secret ingredient to the Philosopher's Stone was a mass of live humans, he marked his body with the transmutation symbols that were needed to absorb lives, and he became a living Philosopher's Stone. The lives he absorbed were of the people who died in the Ishval massacre. When he and Scar tried to flee from the mass killings, the state alchemist Solf Kimblee pursued them, and used his alchemical powers to give Scar the unusual mark on his forehead as well as to amputate his right arm. Scar's brother dispatched Kimblee by robbing him of the power-enhancing Red Stone he was wielding, and then fused his own right arm — on which was tattooed a portion of the transmutation circle which creates the Philosopher's Stone — to Scar's body before dying.