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.
Although the T-1000 was frozen and then shattered, its fragments melted due to the heat from within the steel mill. Its liquid metal form reconstituted itself and continued to pursue the Connors, albeit slower than before. The transition from extreme cold to extreme heat causes the T-1000's polymimetic form to malfunction, causing it to partially fuse to the environment and making it difficult to maintain a single shape.
The T-1000 battles against the T-800 and seemingly defeats it, then corners John and Sarah on a platform suspended above a pool of molten steel. Sarah tries to shoot the machine over the edge of the platform but runs out of ammo, but the T-800 reappears from above a large gear, having rebooted using a backup power cell, and fires a round from its grenade launcher at the T-1000. The liquid metal android is blasted off the platform and plummets into the white-hot pool below, thrashing around as though writhing in anger and pain, before it is completely dissolved by the steel.