For the antagonist from Terminator 2: Judgment Day, click here.
The T-1000 was an advanced android assassin created by the malevolent artificial intelligence Skynet. It appears as a tertiary antagonist in Terminator: Genisys, using its ability to mimic the forms of others to get close to its targets. It is portrayed by Byung-hun Lee.
This T-1000 was sent back in time by Skynet to 1973 on a mission to kill Sarah Connor while she was still a child. While it succeeded in killing Sarah's parents, its mission was interrupted by the arrival of the Guardian, a re-programmed T-800 sent back by an unknown party to protect Sarah. The Guardian rescued Sarah and fled with her, but the T-1000 would eventually track her down again.
In 1984, the T-1000 was in Los Angeles awaiting the arrival of Kyle Reese, a Resistance soldier sent back to protect Sarah. Disguised as a police officer, the android almost succeeded in terminating Kyle but was stopped by Sarah and the Guardian. Sarah and Kyle fled together in an armoured truck, but the T-1000 was able to track them by shedding a small fragment of itself and planting it on the truck. It followed them to an abandoned warehouse and used another sliver of its own polymimetic alloy to reactivate an inert T-800 that the Guardian had incapacitated earlier. It also immobilized the Guardian by forming a spear and pinning the older android to a wall. As the reactivated T-800 went after Kyle, the T-1000 confronted Sarah.
After a brief confrontation, Sarah lead the T-1000, who impersonated Kyle, into a large room with barrels of highly corrosive acid under a grate on the ceiling. It tried to confuse Sarah with the real Kyle, but she guessed (correctly) by shooting one of the Kyles in the foot. She the shot acid containers on the ceiling, which corroded the Terminator to almost the point of immobility; this did not completely stop it, as enough polyalloy remained to still form a semi-coherent form that it used to slash at Sarah. It only got a couple of strikes in before Pops, who had since freed himself from the T-1000's spike, finished it off by holding it under the acid shower until it corroded into nothing.