One of the primary characters in the initial installment of the Marathon series, Leela was one of three A.I. constructs installed aboard the UESC Marathon, a colossal space station which, prior to its capture by hostile alien forces, serviced a human colony in the Tau Ceti system. While Durandal was assigned menial tasks such as overseeing door functionality and other automated processes, and Tycho was restricted to maintaining the ship's science and engineering network, Leela could be considered the ship's main A.I., and thus, in 2794, when the station came under attack by the Pfhor, organized coordination of the Marathon's defenses fell largely to her. In communications with the player character, Leela is portrayed as a helpful if somewhat dispassionate individual who is unwavering in her dedication to the task of protecting Tau Ceti's human colonists and preserving the Marathon and its crew.
Defense of the Marathon (Marathon)
Leela contacts the player character almost immediately after he boards the Marathon, establishing herself as a friend and acting thereafter as an adviser on how best to proceed while also providing the player with numerous objectives intended to improve the station's chances against the Pfhor. Early on, she discovers that the station's other two A.I.s, Durandal and Tycho, will be unable to assist them in their endeavor; according to Leela, Durandal has begun to show clear signs of rampancy, and is therefor either unable or unwilling to help them, while Tycho was completely disabled in the initial attack. Complicating matters, she reveals that she was also damaged by the Pfhor's assault, and that the S'pht who accompanied them are actively in the process of seeking to take her offline. Nevertheless, she is still able to successfully aid the player in defending the ship while also seeking to curtail Durandal's rampant growth. That is, until the player is abducted by Durandal as Leela attempts to teleport him to another area of the ship.
For a time, the security officer is held at the whim of Durandal, and though Leela is eventually able to rescue him, by this time both the situation aboard the Marathon and her own personal status have taken a turn for the worse. Convinced that the S'pht will soon succeed in compromising her, Leela privileges Durandal with her plans for the station's defense, and shortly thereafter the player looses contact with her. Durandal and the officer are able to reverse the station's fortunes by destroying the control mechanism the Pfhor devised to dominate the S'pht, which causes their former slaves to revolt against them. With no further reason to hold her captive, the S'pht release Leela, and without the help of the S'pht the Pfhor are soon forced to surrender. Though the colony itself survived with surprisingly few casualties, Leela is somewhat distraught by the fact that there were cyborgs hidden among the colonists whom she was previously unaware of, and furthermore she shows some concern regarding the intentions of Durandal, who absconded at the helm of a Pfhor ship.
Though she plays no active role in the later iterations of the Marathon series, the ending of Marathon 2 sheds some light on Leela's fate after the events of the first game. It is mentioned that the Marathon was attacked a second time by the Pfhor, and that their scientists used this opportunity to strip Leela from the ship, moving her to one of their own vessels. Though they had intended to bring her to their homewold, the ship housing her was lost to a band of Nar privateers, who in turn sold the craft to the Vylae. The Vylae then attempted to reconstruct the A.I., which crashed a network spanning fifteen planets after Leela subsequently went rampant. The incident has since become infamous, and the Vylae have to date been unsuccessful in completely expunging Leela from their planetary network.
- According to Greg Kirkpatrick, the Marathon series' lead writer, Leela was inspired by the Doctor Who character of the same name. When asked what shared qualities the two have, Kirkpatrick responded that both display "determination, loyalty, and strength", and also that both tend to take things at face value.