The Cyberdyne Systems Model 101 Series 800 Terminator was sent by Skynet in 2029 to Los Angeles in 1984 to kill Sarah Connor, the future mother of John Connor, the leader of the future human Resistance. It was the first of the Infiltrators sent back on assassination missions by Skynet, and is arguably the single most significant Terminator unit as it inadvertently "fathered" Skynet in its journey through time, much like how Kyle Reese fathered John Connor in his.
The Terminator
After emerging from the time displacement sphere, at 1:52 AM on May 12, 1984 at the Griffith Observatory, the naked Terminator encountered three punks roaming the streets and forcibly demanded their clothing. At some unspecified time later, in the earlier hours of the morning, it went to a gun shop to acquire weapons for its mission, killing the shop's proprietor. The Terminator then checked a phone book for a list of Sarah Connors, finding a total of three. It proceeded to kill Sarah Ann Connor and Sarah Louise Connor before tracking down its intended target, Sarah Jeanette Connor, in Tech Noir. The Terminator nearly succeeded in killing her. However Kyle Reese, a soldier sent by the future John Connor, helped Sarah to escape.
A chase ensued and the Terminator was injured in a car crash, damaging its arm and left eye. After removing the useless flesh eye and revealing its cybernetic eye, the Terminator wore sunglasses to hide its features. It then went to an LAPD police station to terminate Sarah, and while it went on a shooting spree, it failed to eliminate Connor. It later tracked down Sarah and Kyle at the Tiki Motel, but the two escaped. The Terminator then pursued them on a high speed motorcycle through a tunnel, and then drove a gas truck while Kyle used a pipe bomb to destroy it. However, while the truck was destroyed, the Terminator was not. Its living tissue was burned away by the fire and its endoskeleton was revealed. It chased Kyle and Sarah into a factory, where Kyle attempted to blow it up, but it still survived. Sarah Connor finally destroyed the robot when she crushed it in a hydraulic press, just seconds before it was about to choke her.
Terminator 2: Judgment Day
The same arm that came so close to killing Sarah Connor and its CPU had survived the hydraulic press. Dr. Miles Bennett Dyson, a cybernetics scientist and a high-ranking employee of Cyberdyne, was tasked with creating a new neural-net processor from these two pieces of unknown-sourced advanced technology.
Miles studied the processors and was able to build a revolutionary new brand of automated systems, a more-advanced form of artificial intelligence and making other existing computer systems obsolete in comparison. The project eventually reached the point where he nearly completed a prototype of the processor. Like how Kyle Reese's entrance into the timeline altered the fathering of John Connor, the introduction of the Terminator's remains altered and accelerated the rise of Skynet, introducing another alternate future revolving around a predestination paradox. The remains were recovered by John Connor (Now thirteen years old) and his mother Sarah and destroyed by being thrown into a vat of burning steel in an attempt to change the future and eliminate Skynet once and for all.
Notes
This T-800's endoskeleton is used as the image for the T-831 "Heavy Combat Chassis" from The Terminator Collectible Card Game.
Behind the Scenes
Lance Henriksen was originally cast in this role, but was passed over in favor of Schwarzenegger. O.J. Simpson was also considered, but was passed over by James Cameron because he couldn't imagine "such a nice guy playing the part of a ruthless killer."
T-800's human face is used as the digital make-up for the prototype T-800's face in the film Terminator Salvation.