John Malleus

 was the chief scientist of Vault 92.

He was in charge of implementing the experiment of Vault 92 and is initially intrigued and optimistic about the results of the test. When the killings began, however, he quickly got to the bottom of the situation and discovered that Rubin had been brainwashing the musicians without controls or safety measures, with "combat suggestions" that came from Vault-Tec itself, turning the residents into violent, primal animals.

His conscience may have cost him his life, as Rubin's personal logs stated that the professor was an impediment to the project and was to be removed.

Appearances
This character is mentioned in Fallout 3 but does not actually appear in the game.

Behind the scenes
Malleus is quite probably named after one of the three auditory ossicles (the 3 smallest bones in the human body, located in the middle ear) which transmit sounds from the air to the inner ear. The malleus is the "hammer" in the set of "hammer, anvil, and stirrup," so named after their shapes.