Gold-Toothed Doctor

"The Alchemist Doctor" or "Gold-Toothed Doctor" (real name unknown) is an old man who is in possession of his very own Philosopher's Stone, as well as one of the few responsible for Wrath's creation. He is privy to Amestris' top secrets and carries out Father's orders in a ruthless fashion.

Appearance
The Doctor is a short old man who has one golden tooth, short auburn hair, and mustache. He can normally be seen wearing a white lab coat along with his signature glasses. In numerous occasions, his eyes have also been shown to be disturbingly unfocused, looking out towards the corner of his eyelids.

Part in the Story
A younger Doctor is first seen in a flashback scene, some sixty years before the start of the series, when King Bradley becomes a Homunculus. The Doctor is shown to have been the one directly responsible for injecting a liquid Philosopher's Stone into the human candidate's body. He makes his next appearance during the current timeline alongside General Raven in Briggs, where he is taken to heal Solf J. Kimblee from his battle wounds against Scar.

During the attack on Central City, Edward Elric, Roy Mustang, Scar and Riza Hawkeye are searching the maze-like underground passages for Father's room when they unexpectedly come across the Alchemist Doctor. He greets them shortly before sending numerous sword-wielding men after them. These men are revealed to be failed Führer candidates from decades past and as such possess almost as good fighting abilities as Wrath himself. After a short fight, the Doctor activates a Transmutation Circle which -- working in accordance with other scattered circles around the city in each of the Five Central Laboratories, sucks Edward, Alphonse, and Izumi Curtis to The Gate.

The Führer soldiers restrain Mustang, Hawkeye and Scar while the Doctor tries to persuade Mustang to willingly perform Human Transmutation, yet Roy refuses. Reaffirming the fact their time is short, the Alchemist Doctor orders one of the soldiers to slash Hawkeye across her throat, causing her to bleed heavily. Mustang once again refuses to do Human Transmutation to save her on her own dying orders. With the sudden arrival of back-up, the Doctor is then subdued by Jerso and the others defeat the rest of the Führer soldiers. Relief, however, is short, as both Wrath and Pride arrive on the scene. Wrath pins Mustang to the ground by stabbing swords through his palms.

The Doctor is praising Wrath for his aid when Pride unexpectedly stabs him through his back to use him as a raw human sacrifice in the process. A Transmutation Circle under them then activates and Pride and Mustang both disappear through it. After the smoke clears, the only thing left of the Gold-Toothed Doctor is a bloated, disgusting mass of flesh that barely resembles him. Ironically, he is transmutated into a byproduct of the Human Transmutation he desperately craved. His only features left unchanged were his golden tooth and crooked eyes.

Powers and Abilities
The Alchemist Doctor has performed numerous experiments injecting Philosopher's Stones into human bodies, and as such, he is able to use them personally to great proficiency. With a Philosopher's Stone, he can heal others like Solf J. Kimblee in a matter similar to that of Dr. Marcoh, and is able to command the failed Führer candidates to do his bidding. Probably his greatest feat is to perform a special human transmutation so as to gather the Human Sacrifices and teleport them to wherever he so desires. He also seems to be highly intelligent, as he was able to predict where Edward's group would be going to set up an ambush for them.

Trivia

 * As seen when he treats Kimblee in the 2009 anime and the manga, the doctor is missing a tooth in the present time. However, when he is shown underground much later, the tooth is suddenly back in place in the anime. Even stranger is that it's still consistent at first in the manga, but then the tooth reappears there too.
 * In the original Japanese version, the doctor talks very slowly, almost lethargically, but yet still highly enthused over each word he says, while in the English dub, he speaks much more fluently and actually rather quickly.