Jackson "Black Dog" O'Rourke.
Eldest descendant of the O'Rourke line out of Vault 13. A brief history will follow.
In Fallout 1: Jacob "Black Dog" O'Rourke began his life as a mercenary. After initially being released from Vault 13 in order to recover a water chip, the would-be savior never returned or checked in. His initial search of Vault 15 yielded no results... save for that the place was empty. He meandered back toward a settlement he had passed along the way, learning that the dwellers from that vault had abandoned it long ago after fracturing into a number of violent factions. After a brief stay in Shady Sands, Jackson O'Rourke moved along... locating the camp of the raider clan styling themselves the Khans. Jacob befriended these villainous murderers, using their stockpiles to arm and armor himself before eventually heading further south into Junktown.
It was here that Jacob O'Rourke earned his fortune. In a fluke chance at a slot machine, Black Dog O'Rourke took the jackpot... instantaneously becoming the wealthiest man in Junktown. Rather, after the very public gunfight with Gizmo... the casino's owner... he was the wealthiest man in Junktown. He used this wealth to found Black Dog Security, a mercenary firm which operated out of the Hub until the detonation of the nuclear bomb at the Cathedral. Where he went from there is unknown... as records following events after that point were poorly maintained. It is known that he eventually died, leaving a son: Joseph.
In Fallout 2: After stumbling across a half-dead tribal called 'The Chosen One' near the primitive village of Arroyo, Thomas O'Rourke found himself taking up the family business of 'hired gun' despite his father Joseph's attempts to steer him away from that path. Working under the name of "Black Dog", O'Rourke assisted the wounded tribal in locating and recovering a device called a Garden of Eden Creation Kit... supposedly capable of restoring life to the dead and desolate wasteland. When the device was recovered, however, they returned to Arroyo just in time to learn that there had been an attack.
An organization known as the Enclave had abducted the tribal citizenry, flying them away over the sea to their offshore headquarters. The tribal remained behind... working slowly to repair the damage done to his village. Thomas, meanwhile, found himself being fed information by observers representing the Brotherhood of Steel, an organization with which he had never had much experience before. Despite heavy opposition, he eventually acquired the means to reach the offshore headquarters: The PMV Valdez. It took a great deal of manipulation in order to get the Key FOB and NavCom pats required to operate the vessel... but eventually he managed. The result was the rescue of those individuals abducted by the Enclave for experimentation... and the utter destruction of their base through a detonation of their nuclear reactor.
After the events of this venture, the abductees returned to Arroyo. Thomas O'Rourke eventually settled down in Modoc, a small farming town suffering from severe crop failure. He eventually married Miria, the daughter of local slaughterhouse owner Grisham. Notable achievements beyond this include the destruction of the Slaver's Guild in The Den, the revitalization of Modoc's crops through use of the second G.E.C.K. recovered on the Poseidon Oil Derrick, and re-establishing the name of 'Black Dog Security' throughout the Northern California Area. He was awarded honorary status as an NCR Ranger and continued to fight against slavery and lawlessness until his death. Thomas "Black Dog" O'Rourke was survived by wife Miria, sons Martin and Jackson, and daughter Kelley.
In Fallout 3: Martin "Black Dog" O'Rourke took a job working for some environmental biologists from the NCR interested in heading East. It was supposed to be a long-term assignment... but somewhere along the way things fell apart. While the eggheads were busy fighting over where they wanted to head next, marauders swept in and took them out. By the time Martin got back, the team was dead and everything of value was stolen. He continued onward until he bumped into a group of 'settlers' headed south. For a cut of their supplies, he provided himself as a guard.
Eventually he wound up in the Capital Wasteland, and did in fact live in Megaton for some time. After getting caught between Supermutants and Talon Company outside the Statesman Hotel, he found himself aiding a group known as Reilly's Rangers. Once he'd cleared the way upstairs and helped repair the elevator, the unit descended to the first floor... and into an ambush. Just as they were exiting the door, a Supermutant Master stepped out of a nearby doorway and fired a missile, killing Butcher and severely injuring Martin O'Rourke. As it had been he who stated that the path was clear... he took the failure personally. When he later learned that Butcher was in fact romantically involved with Reilly, Martin O'Rourke decided to stay on with the Rangers in an attempt to make amends. He eventually became involved with Reilly himself, and remained a constant presence in the Capital Wasteland until his death in 2315 at the age of 60. He was survived by Reilly and two daughters, Michelle and Mary O'Rourke.
[Edited For Minor Spelling Errors and Historical Accuracy]