Tim Marcoh (ティム・マルコー, Timu Marukō), formerly the "Crystal Alchemist", was the leading researcher in the military's Philosopher's Stone creation project. After sacrificing a number of innocent Ishbalans during the Ishbal Civil War to create new stones, he fled the military with some imperfect stone samples. He settles down in a small country town where he uses his stones to heal the sick under the identity of "Doctor Mauro". He is later found by the Elric brothers, and he directs them to some of the research he left behind in Central to help them in their search for the Philosopher's Stone. In the anime he is soon afterwards taken into military custody, only to be killed by the homunculus, Lust.

In the manga, Marcoh takes a larger role in the ongoing story. When first found by the homunculi he is kept under house arrest, forced to stay put and alive or risk the destruction of his town. He is later taken into their custody to be used in their future plans, and is kept locked up deep below Central. While there he is found by Scar. Seeing Scar as a means to an end, he tells Scar of his involvement in the Ishbalan War in the hopes of being killed in vengeance. Scar, instead, only disfigures his face beyond recognition as a disguise, kidnaps him, and forces him to help in bringing down the homunculi.

Source: Wikipedia