Brian Virgil

Dr. Brian Virgil (Institute username Virgil.B) is a super mutant living in the Commonwealth in 2287. Living initially in the rocky cave, he helps the Sole Survivor find a way into the Institute.

Background
Dr. Brian Virgil was a member of the Institute at some point before 2287. He was in charge of a project involving the Forced Evolutionary Virus and the creation of super mutants in the BioScience Division. Virgil took control of the program after his predecessor, Dr. Syverson, passed away. Overcome with guilt from the pain and suffering he had inflicted on so many innocent people, he decided to leave the Institute. Virgil destroyed the lab equipment and all of the research, which is logged as "Incident V" in terminal entries. He then escaped the Institute, afterward infecting himself with a unique strain of FEV in order to survive the high levels of radiation in the Glowing Sea. The Institute was aware of his presence in the Glowing Sea and sent Kellogg to kill him, a mission that would ultimately never be carried out.

Quests

 * The Glowing Sea: After heading through the Glowing Sea and being asked by the Sole Survivor for information on the Institute, Virgil will ask the Sole Survivor to recover an experimental serum that he claims will make him a human again, but isn't sure if it exists or not. The player character must agree to this if they want to complete the quest and continue the main story line, however, the Sole Survivor need not follow through with this promise.
 * A Loose End: Unless convinced to spare him through a Charisma check, Kells will order the Sole Survivor to kill Virgil.

Effects of player's actions

 * After getting the serum, the player character has two options:
 * They can simply give Virgil the serum, and certain companions will react differently to this choice. For example, John Hancock, Piper, Nick Valentine, Codsworth, Deacon and Curie like the player's choice to cure Virgil, but Danse won't like it at all; this is due to what happened to his friend Cutler. Strong also won't like it as he prefers being a Super Mutant and is angry with the doctor's ambitions to cure the others.
 * They can also lie to Virgil through a sequence of three speech checks, claiming that the serum wasn't there. The checks' difficulty increases with each one. After the first two checks the player character still has the option to give the serum to Virgil through breaking and reinitiating dialogue with him. After the third speech check Virgil requests the player character to kill him and Virgil's Cure will fail. If the player has visited Swan's Pond, and read the notes there, they can ask Virgil if he remembers Edgar Swann after the first speech check. This will lead to a medium speech check to convince him to end his life (bypassing the hard check).
 * If the player character gives Virgil the serum and waits three days, they can go back and see that Virgil is now a normal human. After this, all the items inside the cave become available for looting.
 * If the player character is wearing a power armor helmet with a Targeting HUD mod when returning to complete the quest The Glowing Sea, the Sole Survivor will immediately fail the quest upon re-entering rocky cave with the serum. Remove the helmet before entering the cave.
 * If upon first entering and leaving the Institute, even if the player does not get the serum, the player character waits before bringing the serum to Virgil for around a week, Virgil is then found completely turned hostile and the quest "The Glowing Sea" will immediately fail upon re-entering rocky cave.
 * If the Sole Survivor destroys the Institute, Virgil will confront them about it the next time they enter his cave. No matter how the Sole Survivor responds, he states that "innocents died," and replies that they have nothing more to speak about, and tells them to leave his cave. The Sole Survivor can stay however long they want, regardless of what Virgil says, as he will not turn hostile.
 * If the Sole Survivor destroys the Institute before giving the serum to Virgil, he may turn hostile after a monologue.

Appearances
Virgil appears only in Fallout 4.

Bugs

 * He will turn hostile (together with his protectron and turrets) when returning to him (when returning him the serum, or once he is cured) if the cave is entered in power armor.
 * This is caused by the "Targeting HUD" helmet upgrade (others upgrades may or may not affect this). Simply unequip the helmet on the power armor before entering the cave.
 * The Tesla coil power armor upgrade may attack Virgil's turrets upon returning to the cave towards the end of the quest, making Virgil and the turrets hostile.
 * All of Virgil's super mutant textures are extremely low-res even on high-end gaming rigs with all graphics settings set to maximum.