Although physically similar to the T-800, the T-850 possesses a number of noticeable differences; The T-850's appearance is an aged version of the T-800 and lacks the sense of humor exhibited by its predecessor. It almost seems to stand up for itself when it replied that it is a "cybernetic organism", not a "Robot", as John had stated. Although originally programmed to follow any and all orders from Kate, it could override this default programming and trap her in the back of her truck against her wishes. It states that one of its basic subroutines deals with human psychology, and despite its lack of humor is still able to make an emotional connection with John when he fights the T-X's reprogramming of his systems and again later when he says goodbye to John.
Terminator 3: Rise of the Machines
It approached Connor in a veterinarian clinic where Brewster worked and took the two with him in the back of a van to escape the T-X, a new, highly advanced Terminator. While driving, John asked him about its memories, assuming that this would have the same memories as "Uncle Bob". It stated that the Terminator sent from last time was a different unit. He also tells John that a T-X was sent back through time to eliminate his lieutenants. As well as that his efforts in the second film did not stop Judgment Day, but merely postponed it and that the T-X is designed to be capable of defeating other Terminators.
At a graveyard, the three went to Sarah Connor's grave. The Terminator dropped her coffin to find weapons inside. When the police arrived, they got out and confronted the T-X. Later, at a campsite, the Terminator revealed that if the T-X failed to kill John, it would kill John's future officers as secondary targets, including Kate's father, Robert Brewster. While driving, the Terminator revealed that he follows Kate's commands rather than John's, unlike the Terminator in Terminator 2 as it was Katherine who sent the machine from the future, not John, because the Terminator killed John in 2032 before being captured and reprogrammed by the Resistance and he was chosen by Skynet for infiltration due to John's emotional attachment due to his boyhood experiences.
In the Cyber Research Systems facility, the Terminator battled with T-1 units. It also fought the T-X, but lost, resulting in it being infected by the T-X's nanites that take control of its body. Controlled by the T-X, the T-850 began to attack John and Kate, but shut itself down to prevent itself from killing John when he confronted it with the conflict between its current actions and its primary programmed mission to ensure John and Kate's survival. Later it rebooted, regained control of itself, and again battled the T-X at Crystal Peak after hijacking a helicopter to follow John and Kate. Although crashing the helicopter on the T-X only damaged its legs and its external appearance, the damage delayed it long enough for John and Kate to retreat into the Crystal Peak underground bunker to wait out the now-inevitable nuclear war. When the T-X attempted to follow them, it managed to detonate its last hydrogen fuel cell to destroy itself and the T-X, ramming the power cell into its opponent's mouth, resulting in a massive detonation, its last words being to inform the T-X "You are terminated". Realizing that the Future War has now begun, John muses that all he can do now is follow the Terminator's example and never stop fighting.
Terminator 3: The Redemption
At one point while fighting through the Cyber Research Facility, the T-850 is thrown into a prototype time machine, sending it into a future where the T-X succeeded in its mission and humanity has been terminated. However, the T-850 was able to find another time machine in that era and return to the present, where it proceeded to find and rescue John and Kate.
It is revealed that after the explosion of the hydrogen fuel cell, the T-850 survived, but it was heavily damaged and barely "alive". John Connor removed its CPU upon finding the T-850. Several years later, John insert the chip into an FK Reaper during the Future War. Thus, the Terminator is brought back to be fully operational again, fighting along with the Resistance, albeit in a very different body.
- Its series, T-850, is identified in the novelization of the film, in which he is referred as a T-101 instead.
- Terminator 3: Eyes of the Rise
- Terminator 2: Infinity (Mentioned only)
- Terminator: Revolution (Flashback)
- Terminator Salvation: The Final Battle