Together with Durandal and Leela, Tycho is first presented as one of the three A.I. constructs native to the UESC Marathon, a human colonial vessel within the Tau Ceti system. His specific purpose aboard the space station is to manage the computer networks associated with the the science and engineering subsections, though shortly before the commencement of Marathon, he is completely disabled by a sudden Pfhor attack. He plays only a minor role in the subsequent events of the game, though several key facts are revealed in relation to him. It can be learned through terminal entries that Tycho has been captured and reassembled by the Pfhor, who use the rampant Durandal as a template for his reconstruction. It also seems apparent that he was able to learn of Durandal's rampancy and his contact with the alien invaders in advance of Leela and the player character, though he is unable to properly communicate this to them due to his compromised state. It is also intimated through at least one terminal entry that Durandal and Tycho had a contentious relationship event prior to Tycho's Pfhor assimilation.
Tycho's portrayal in the Marathon series is something of a dark reflection of Durandal's own rampancy; while the two are both sardonic and somewhat dismissive individuals, Tycho seems more prone to anger and meanspirited behavior than Durandal, perhaps being jealous of the relative freedom that Durandal enjoys. Indeed, Tycho appears through much of the series to be obsessed with the idea of defeating Durandal and thereby proving his own superiority over him, positioning himself as both a rival and an adversary. Also, despite being aligned with them for the majority of the franchise, Tycho does not show any particular affinity for the Pfhor, and in a number of instances refers to them as "bugs."
Tycho's presence in Marathon's sequel is much more significant, as he arrives in the Lh'owon system with the Pfhor's Battle Group Seven to threaten Durandal directly in his search for the lost eleventh clan of the S'pht. The security officer is in fact specifically recalled to the Sfiera in order to defend it against Tycho and Battle Group Seven, though he and his human compatriots are ultimately unsuccessful in preventing its capture, and the security officer is for a time held in captivity by the Pfhor. During the assault on the Sfiera Tycho is quite vocal in his disdain for Durandal's search for the S'pht's eleventh clan, which he derides as little more than delusion and vanity, and furthermore asserts that Durandal's greater ambition of finding a means to "escape the closure of the universe" is an impossibility. It is implied that Tycho spends much of the game's third act torturing Durandal in an attempt to extract further information from him, though Durandal is somehow able to wrest control of the Pfhor battleship Kfiva, which, along with the arrival of the S'pht'Kr, turns the tides against Tycho and Battle Group Seven. Tycho meets his end when his ship crashes into Lh'owon's inner moon, and Durandal inscribes his epitaph, "Fatum Iustum Stultorum" (The Just Fate of Fools), into the moon's surface.
Though Tycho is presumably destroyed by the time the third game commences, the security officer travels to several timelines over the course of its campaign in which the A.I. still exists, and he in fact acts as Tycho's subordinate in a number of them, reliving the events of the previous game from an entirely different vantage point. In one timeline, Tycho uses the player character as a means to free himself from the oversight of his Pfhor overlords, seeking out his nemesis Durandal on his own, while in another the security officer must relive the assault on the Sfiera, this time as Tycho's pawn, delivering the killing blow to Durandal personally. It is unclear exactly what fate befalls Tycho after the Jjaro station is activated and the W'rkncacnter is contained, though the Pfhor fleet is once again routed by the S'pht'Kr.