The former head of the Institute's biochemical division, Brian Virgil could no longer stomach the experiments of his colleagues, and as a consequence, destroyed as much of his F.E.V. research as he could, and then deserted the organization to hide out within the Glowing Sea. His escape to the Glowing Sea was in order to elude his Courser pursuers, in which he made this escape possible by intentionally or unintentionally transforming himself into an Institute variety of super mutant, which allowed for him to become immune to the fatal levels of radiation present within the Glowing Sea. Unfortunately for Virgil, F.E.V. has long-term effects on the human mind and body, the least of which being his inability to type properly due to over sized fingers and the greatest the slow loss of faculties, especially analytical thinking.
Lance Captain Kells will request the termination of Virgil, due to his combined status as a former Institute scientist and super mutant. The player has to kill Virgil, if they can't pass a speech check to convince the Captain otherwise (such as after turning Virgil back into a human).
↑Brian Virgil: "It wasn't exactly my best idea, but turning into one of these hulking monstrosities was the only way to... uhh, well to get here. At least I avoided some of the side effects, and retained my faculties." (Brian Virgil's dialogue)