Tim Marcoh

, formerly the, was the leading researcher in the military's Philosopher's Stone creation project.

History
After sacrificing a number of innocent Ishvalans during the Ishval Civil War to create new stones in Laboratory 5, 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 the National Central Library to help them in their search for the Philosopher's Stone.

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, Envy takes great pleasure in tormenting Marcoh by constantly reminding him the Homunculi would massacre his hometown if he ever escaped. After some time as a prisoner, he is found by Scar.

Seeing Scar as a means to an end, he tells the Ishvalan of his involvement in the Ishval Civil 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. While on the run, he is eventually discovered by Envy, who vows to take him back to Central but not before killing hundreds in a near-by village as revenge for Marcoh's escape. Knowing this, the Crystal Alchemist attacks Envy using his hidden transmutation circle to critically damage the Homunculus' core stone. Later, after Kimblee springs Pride from his dome prison, Marcoh takes part in a ruse to deceive the two along with Heinkel and Alphonse. Alphonse gives Marcoh the Philosopher's Stone that Heinkel gave him, which he then used to heal Heinkel's wounds while Alphonse acted as a diversion. He is last seen with Dr. Knox, telling Colonel Mustang that he will use the Philosopher's Stone to give him his eye sight back on the condition that he improves conditions for the Ishvalan people, restores their homeland, and allows himself to stay there as a doctor, to which the Colonel accepts. In the manga he accepts and lets him help the Ishvalans.

2003 anime
In the first anime series, Marcoh plays a significantly lesser role. After being taken into custody by Juliet Douglas, he is confronted by Lust. She questions him about the information he gave to the Elrics and subsequently murders him. His body is implied to have been eaten by Gluttony.

He later makes a brief cameo in the penultimate episode as one of the forms Envy uses to toy with Edward.

Abilities
Dr. Marcoh is one of the oldest known alchemists of the series and as such has incredible knowledge regarding alchemy. His most notable knowledge is related to the creation of the Philosopher's Stone, knowledge given to him by the homunculi. After numerous experiments with their creation, he is also able to destroy them, an ability which proves effective when fighting Envy.

Due to his elderly state, Dr. Marcoh is not able to use alchemy in combat, but rather he proves to be skilled when it comes to support tasks such as healing or deciphering codes. He is also very skilled in medicine, as more than one person has asked for his assistance, although his healing abilities may be possible through the use of the Philosopher's Stone, rather than a unique ability like Alkahestry. He also posesses the unique ability to destroy Philosopher's Stones with a single transmutation, giving him the power to cripple or kill Homunculi with a single touch.

What his epithet as the "Crystal Alchemist" means is unknown, but it is likely connected to the Philosopher's Stone in some way.

Regardless of his inability to fight, his knowledge makes him a valuable ally.