T-1000

The T-1000 is a Terminator, a much more sophisticated killing machine than either the T-101 or the Terminatrix, and/or TX. He is made of some kind of liquid metal, able to formulate itself into sharp objects or impersonate anyone it has touched.

Impersonations
John Connor's foster mother Sarah Conner Motorcycle Cop Police Officer Security Guard (among others)

The T-1000 was eventually killed by being blasted by a grenade launcher fired by the T-101, and fell into a pit of molten lava, effectively destroying all trace of the foul Terminator.