|This article is about a non-canonical topic in the Metal Gear series.|
O'Brien was a United States Navy captain. Multiply decorated in the Persian Gulf, Europe, and Africa, he was praised in the mass media as a competent and noble-minded military man who was well-liked by his fellow soldiers.
In the late 2000s, Captain O'Brien discovered that the former leader of Dead Cell, Colonel Jackson, had hatched a plot to restore his unit's reputation, following his incarceration on corruption charges. Jackson had ordered his successor Vamp to commit a series of "revenge" murders to make the public wrongfully believe that he had been framed and unjustly imprisoned. O'Brien took advantage of the situation for his own political advancement, and instead had Vamp place himself and Dead Cell under his command, after threatening to expose the truth of Jackson's conspiracy.
O'Brien later led a top-secret joint exercise between the Navy SEALs and Dead Cell at the marine decontamination facility "Big Shell," off the coast of New York. During the exercise, Dead Cell and a team under their command portrayed terrorists, while the SEAL team acted to suppress them. O'Brien ordered Vamp to kill his political opponent in the exercise, Marine Commandant Scott Dolph, as a test of his loyalty, but Vamp chose to feign servitude and planned to kill O'Brien instead.
As the exercise drew to a close, O'Brien was forced to go into hiding after Dead Cell leader Vamp went on a murderous rampage through the facility. Hiding in Shell 2, O'Brien had SEALs stationed on the Shell 1-2 connecting bridge and barricaded himself in a room protected by an electrified walkway, but these attempts failed to prevent Vamp from confronting him. O'Brien was then tortured by Vamp, suffering multiple severe cuts, before the latter left him for dead. He was subsequently found by Solid Snake (disguised as SEAL Lieutenant J.G. Iroquois Pliskin) and told him that Vamp's "lynching" was revenge for Dead Cell's sullied reputation, having been exploited in the past by government and military figures to carry out their dirty work. Revealing that Colonel Jackson's corruption case was watertight, and warning Snake to escape and call for backup, O'Brien passed away shortly thereafter, despite Snake's efforts to treat his wounds.
Behind the scenes
O'Brien appears in the Snake Tales scenario, "Dead Man Whispers," included in Metal Gear Solid 2: Substance. His character model reuses that of the Navy Captain from the Plant chapter of Metal Gear Solid 2: Sons of Liberty. In addition, depending on how much time the player takes to find him, O'Brien will either die after telling Snake that Jackson's corruption case is "watertight," or live long enough to inform Snake that Vamp is being deceived as well.