A liquid metal Terminator.
" What is it? "
" The T-1000 "
A terminator (basically a robot assassin from the future) that is constructed entirely out of mimetic polly-alloy (a self-healing liquid metal). It's self healing liquid nature means it is nearly completely invulnerable to physical harm. It can also shape shift into anything it touches, as long as that thing has a similar mass. They are equally as strong as their T 800 predecessor but their shape shifting abilities and more fluid, lifelike movements make them superior in combat. However, they are much lighter than T 800s, so they aren't able to tolerate heavy gunfire for example (though they could just reform afterwards). They can be temporarily stopped by freezing them and smashing them to pieces but they will reform after thawing. It only lethal weakness is extremely high temperatures (over 2500 degrees Celsius).
A unit was sent to the year 1995 in an attempt to kill ten year old John Connor. Luckily, John from the year 2029 sent back a T 800 that was reprogrammed to protect him. The T 800 proved to be a tough opponent but was eventually killed by the T 1000. The T 800 managed to revive itself and shoot a grenade into the T 1000 body. It detonated and before the T 1000 could reform, it fell backwards into a steel mill, where the temperature destroyed it once and for all.
The T 1000 was portrayed by Robert Patrick and appeared in Terminator 2: Judgement Day.
Officer on bike: You alright?
T 1000: Yeah. Say, that's a nice bike you got there.
T 1000 proceeds to kill officer on bike and takes his patrol bike.