The T-1000 (portrayed by Robert Patrick) is composed of a liquid mimetic polyalloy that allows it to copy the appearance of any person it touches. It cannot form complex devices such as guns (it must acquire firearms should it need them) but can form solid metal objects from its limbs such as knives and swords. It is also unfazed by gunfire, any wounds it receives immediately regenerate.
After arriving in Los Angeles in 1994, the T-1000 murders a police officer and assumes his identity. It then begins seeking out its primary target John Connor, beginning its search at the home of John's foster parents. John isn't home and so the android seeks the boy around town, using a picture given to him by the Voights to identify him. The T-1000 finds John in an arcade and moves in for the kill but is interrupted by the arrival of a reprogrammed T-800 sent back in time by the Resistance to protect John.
The T-800 and John escape and the T-1000 attempts to reacquire the boy at the Voights' house. It breaks in, murders Janelle and Todd and assumes Janelle's identity, speaking in her voice when John calls home to warn his guardians. However, the T-800 imitates John's voice and discovers that the Voights are dead when it asks the T-1000 about their dog, using a false name. Realising John won't be coming home, the T-1000 heads for Pescadero Psychiatric Hospital where John's biological mother Sarah Connor is incarcerated, intending to kill her and use her identity to lure John into a trap. This plan goes awry as not only do John and his T-800 guardian interfere, but Sarah is already in the process of escaping the institution herself.
The T-1000 loses its quarry and is unable to locate them again until an incident occurs at CyberDyne Systems Corporation. When the android arrives, the Connors and the T-800 are fleeing the police and the T-1000 gives chase, first by helicopter and then by hijacking a tanker full of liquid nitrogen. It pursues its targets to a steel mill where it crashes, spilling the contents of the tanker which freeze the android solid. The T-800 pulls out a pistol and fires at the frozen T-1000, which shatters like glass.
Despite the damage, the T-1000's fragments were quickly melted due to the heat from within the steel mill, allowing its liquid metal form to reconstitute itself and continue to pursue the Connors. However, it was now moving much slower than before. The transition from extreme cold to extreme heat had damaged the T-1000's polymimetic form on a level it could not repair, resulting in malfunctions: unable to control its ability to camouflage itself, it would occasionally fuse to objects in unintentional efforts to mimic the surrounding environment, transforming into shapes it did not intend to.
After being prevented from capturing Sarah, the T-1000 battles against the T-800 for a time, and seemingly disables it by impaling its core. Then after cornering John on a platform above a large pool of molten steel, it attempts to lure John to his death by mimicking Sarah and pretending to be helpless, playing on his emotions. This ploy is ultimately undone when John notices that "Sarah's" feet have merged with the gantry beneath her, allowing him to get out of the way just long enough for the real Sarah to open fire: armed with a shotgun, she blasts it again and again, trying to knock it over the edge of the gantry and into the steel, only for her to run out of ammo at the last minute.
Just when it looked as though the T-1000 was now free to murder the two humans at its leisure, the T-800 reappeared, having rebooted using a backup power cell; though badly damaged and no match for the next-generation android at the best of times, it was now armed with a grenade launcher, which it fired squarely into its opponent's torso. Because the T-1000's body absorbed bullets and other missiles on impact, the grenade detonated inside it: with its body temporarily blasted out of shape by the force of the explosion, the T-1000 could no longer maintain its balance on the gantry, and toppled backwards into the molten steel below.
Writhing and thrashing around as if in pain, the T-1000 began transforming wildly, the intense heat quickly destroying its ability to regulate its physical form even as it struggled to find a means of resisting the fatal temperature: from its default form, it then became Janelle, still equipped with the bladed arms it used to kill Todd; then a security guard at the mental hospital; unable to maintain a distinct identity, it then reverted to its liquid metal appearance, briefly sprouting the helmet it wore while driving a motorbike before becoming an abstract silver humanoid. Finally, it lost the ability to appear even as that as its body began to dissolve, tentacle-like limbs flailing in random directions in an attempt to haul itself to safety, additional heads growing from its liquefying torso in futile efforts to escape the steel, but all quickly losing cohesion and collapsing in on themselves.
Finally, it was left only as a single head floating helplessly in the molten steel; bubbling uncontrollably, it opened its mouth in a silent scream and begun to unfurl, its mouth folding over its own face as its physical form underwent a swift final breakdown. When the scream finally came to an end, it was left as nothing more than an almost two-dimensional face that rapidly dissolved into an expanding mass of silvery liquid and vanished into the molten steel.