Created by Skynet, The T-1000 is one in a series of Terminator Robots designed to eliminate humans in the alternate c.2015 machine-dominated future.

The T-1000 is comprised of an odd liquid-metal substance that can adopt the properties of a myriad of substances. It scans and samples molecular data by touch, and stores them for future shape-taking. In this way it becomes quite adept at stealth measures, for it retains the molecular properties of the mimicked item, rendering it completly invisible to scans, visual or otherwise.

Another intresting feature of the T-1000 is the ability to lose a piece of itself, only to have said piece revert to it's natural 'at rest' liquid metal state, and seek out the main body of the assassin droid. This ability, coupled with the ability to roll with the blows (or bullets, as it were) and absorb kinetic energy from projectile weapons by temporarily disforming, makes the T-1000 nigh unstoppable.

The T-1000 was a prototype Terminator at the time of Skynet's demise, being sent back in time in the last moments of Skynet's reign to prevent the fall of Skynet in it's native time. The Time Travel in this continuum only allows biological material (and non-biological material completly enveloped in meat) through, so the T-1000 adopted flesh, and went back. It's mission: Destroy the young John Connor, who in Skynet's final days lead the successful human resistance movement against it.

The T-1000 sought out the young boy immediatly, but Conner was found by another future-borne traveller, this one a reprogrammed T-800 sent to protect him by his own future self. The T-800 secreted him away for safekeeping, driving the T-1000 to find his mother, Sarah Connor, who was at the time imprisoned in an Asylum*

John and the older Terminator figure out that the T-1000 would logically go for Sarah Connor after losing John's trail, and so, make haste towards the Asylum themselves. They make it in time, but only just, as they encounter the T-1000 on premises and make a narrow escape with John's mother.

The T-1000 is thrown off their track fully, and does not find them again until the threesome, plus one Miles Dyson, start attacking the main Cyberdyne Systems laboratory. This lab is basically the mother of Skynet, and so becomes an intresting reversal, as destroying one's mother before she begat something adversarial was Skynet's original Modus Operandi.

The laboratorial infiltrators manage to wreck everything as needed, but not before a legion of policemen (accompanied by the T-1000 incognito as one of their number). In an attempt to stop the saboteurs, the police manage to wound Dyson, who then stays back while the others escape to become a literal Dead-man's switch to the manifold barrels of explosives that Conner and company have left in the lab's records department.

The police evacuate in time, the Connors and T-800 escape to saftey as well, and everything else goes boom really loudly with a rather large ball of fire. As the Connors make a getaway, the T-1000 follows them, and they all end up in a metal refinery after an automotive chase.

The T-1000's liquid nature turns against him for a short while at the refinery, as a truckload of Liquid Nitrogen spills onto him, causing his fluid, morphing self to become rather static and brittle, shattering into thousands of pieces. However, this only delays the mutating beast, for the heat of the steelworks soon melts out the frozen pieces, and it begins to reassemble itself in the fashion mentioned much earlier, reassimilating lost pieces of itself.

The T-1000, after reassembling and then making quite a formidable showing of trickery, unfortunatly was destroyed by the protagonists, whom manage to push the T-1000 into a vat of molten steel. Evidently, being smelted into a mostly-steel alloy doesn't agree with killer robots from the future.

* And not the political kind.