The character was introduced as the main antagonist in the 2003 film Terminator 3: Rise of the Machines, portrayed by Kristanna Loken.

Originally, the T-X's endoskeleton was meant to convey an androgynous shape which would permit the android to assume the superficial traits of both men and women, though later designs veered on it being more feminine.

It is a composite of the T-800 and T-1000, combining the former's solid endoskeleton covered with the latter's liquid metal "mimetic polyalloy", allowing it to take the shape of any humanoid it touches.

Having a solid endoskeleton did solve some of the T-1000's problems, namely being deformed by temperature extremes and explosives while also lacking built-in ranged weaponry.

However, the endoskeleton makes the T-X less flexible than its T-1000 predecessor, in that the T-X does not have the ability to liquefy and assume forms in innovative and surprising ways, including fitting through narrow openings, morphing its arms into solid metal tools or bladed weapons, walking through prison bars, or flattening itself.

The T-X contains a large arsenal of advanced weapons from the future, including plasma cannons and flamethrowers - though it is strong enough to impale a human through the chest with its bare hand.

Although the official novelization of Terminator 2 expanded the origin of the T-1000 and reveals it had onboard nanotechnology (and programmable memory) that was capable of scanning the molecular structure of anything the T-1000 touched, the T-X has a built-in supply of more advanced nanobots in its fingers, which it can inject into other machines, giving it remote control.

Proceeding with its secondary mission, the T-X infiltrates Cyber Research Systems and activates the division's weaponized machines, which kill most of the employees.

The 2003 comic series Terminator 3: Eyes of the Rise depicts the events of Terminator 3: Rise of the Machines from the perspective of the T-X, detailing how it was prepared for its mission before being sent back in time, what its thoughts were during the events of the film, additionally revealing that the T-X survives the film's conclusion in its liquid metal form, albeit no longer being able to take solid form due to a lack of solid material, bar forming a face after John Connor and Kate Brewster have left their bunker to smile at the beginning of Judgment Day.

In the 2004 novel Terminator Hunt, a second T-X is trained by captured resistance members for a jump to the 1960s where she will track the Connor family for the next forty years.