After a T-1000 was sent back in time by Skynet to kill a young Sarah Connor, the Guardian was sent to 1973 to protect her anonymously as its memory files were erased so that no one would know who sent it. Guardian saved Sarah, but her parents were killed by the T-1000. Thus, it raised Sarah by itself and prepared her by teaching her how to defend herself against Skynet's assassins, along with forewarning her about key moments in her future. Over the many years, they spent together and Sarah formed a very strong bond with the Guardian, whom she sees as a father-figure and refers to as "Pops". Over the years Sarah taught the T-800 restraint, leading the Terminator to attack only to disable and works to teach it to blend in though without too much success.
When the (The Terminator Genisys) T-800 sent by Skynet to assassinate Sarah arrived at Griffith Park Observatory in 1984, the Guardian confronted it in a fight. Guardian held it off long enough for Sarah to deactivated it with a .50 caliber round to its chest. The two traveled to downtown Los Angeles to save Kyle Reese, who was under attack from the T-1000. They were able to rescue him, but Kyle was shocked by the Guardian's presence in the vehicle. During a fight, Guardian incapacitated Kyle. When Kyle woke up, Guardian and Sarah explained to Kyle the changes to the future and that they'd been preparing for his arrival for over a decade. As they talk, Guardian detected and shot off a Mimetic polyalloy tracking device on the side of their truck, which would lead the T-1000 to them.
The T-1000 tracked them down and, after a brief car chase, found them in an abandoned warehouse. Upon arrival, the T-1000 impaled Guardian with a pole through the shoulder, pinning and disabling it while the T-1000 went after Sarah, reactivating the T-800 to kill Kyle. Kyle managed to deactivate the T-800 once again and Sarah lured the T-1000 into acid trap to dissolve it. Despite being badly damaged, the T-1000 managed to make it through the acid and strangled her, but by then Guardian had freed himself, grabbing the T-1000 and holds it under the acid to dissolve it. However, doing this dissolved the skin on Guardian's right arm before Sarah neutralized the acid so it would not damage his exoskeleton. Guardian and Sarah then removed the T-800's CPU and dissolved its body in acid so it could not be found and used to create Skynet by reverse engineering as initially happened.
The Guardian and Sarah revealed to Kyle their plan: they intended to use the Time Displacement Equipment that they had developed to travel to 1997 to prevent Judgment Day by destroying Skynet before it was ever created. They needed the T-800's CPU to act as the time machine's operating system, but due to its damaged skin, which would take years to regrow, Guardian could not make the trip as the magnetic field would destroy it. The Guardian chose to "take the long way" and prepare for their arrival instead. While preparing, Kyle remembered "Genisys" from his time jump and told Sarah and Guardian about it. The Guardian confirmed it was possible that Kyle experienced the memories of an altered timeline by experiencing a nexus point while inside the machine and Sarah was convinced to jump forward to that time. The Guardian sent them forward in time to 2017 and remained behind alone, preparing the task which would be needed in 2017.
1984 to 2017
Guardian continued to gather equipment, supplies, and weapons for Kyle and Sarah's use in raiding Skynet in 2017. Over the years, its skin sheath regrew so it appeared human again even if it was elderly. During the preparation period, the Guardian took a position as a member of the construction crew for the Cyberdyne Systems Headquarters to gather intelligence and added Kyle and Sarah's data into a bunker so they could survive the destruction of the building. However, the Guardian was eventually laid off. The Guardian had also kept a collection of photographs and crayon drawings Sarah had made of the two of them when she was a child, along with her old cassette player. Due to age, his servomotors had also begun to degrade and experienced lockups.
When Sarah and Kyle arrived in 2017, the Terminator was not able to intercept them as they materialized above him on top of an overpass in the middle of traffic. He later blamed this on getting stuck in traffic. He watched as they were arrested and was unable to help them. He tracked them to a hospital and infiltrated the building to rescue them, posing as a visitor. After breaking into the security room, the Guardian discovered Sarah and Kyle were being led to the garage by John Connor. Realizing that John had been converted into a T-3000 Infiltrator sent to ensure Skynet's creation, the Guardian fought John. They were both trapped by the magnetic field of a MRI machine. Kyle shut the machine down long enough to allow the Guardian to escape but then switches it back on, leaving John trapped temporarily. They escaped to the Guardian's base on the outskirts of San Francisco.
While preparing for their attack on Cyberdyne, the Guardian explained John's current state to the pair. It cast doubt on Sarah's belief that John could be saved due to the irreversible nature of his conversion but offered a method of defeating him: a magnetic device that could restrain John. The Guardian and Kyle had a slight competition over who could load bullets into clips faster, but the Guardian's servomotors locked up and it dropped some bullets due to the glitch caused by the damage from 1984. It told Kyle that "I am old" and he decided to keep the incident from Sarah. The Guardian left the base to build a device, similar to a cestus, that would restrict the T-3000's move. While preparing his weapon, the T-3000 tracked them down and they were forced to flee on a school bus. During a confrontation on the Golden Gate Bridge, John succeeded in separating the group. The Guardian was able to catch up to them and rescued Sarah and Kyle before they fell off the bridge. The trio were then arrested and taken into custody.
During a one-sided interrogation, the Guardian detected the presence of another Terminator and attacked a member of the police entourage, revealed to be the T-3000 in disguise. The Guardian takes the upperhand this time and was able to hold him off long enough for Kyle to fly them off the roof in a helicopter. John followed in another helicopter and almost succeeded in shooting them down but after losing sight of them for a moment, the Guardian leaped from their helicopter and smashed into John's, causing them to crash into the lobby of the Cyberdyne building.
While Kyle and Sarah feared for the Guardian's safety, he reappeared in time to save him from John by pinning him to a wall with a lamppost. The Guardian informed Sarah and Kyle that he hid a fallout shelter in the construction blueprints to protect them from the explosion. It had been programmed to identify her and grant her access. The three set out to destroy Skynet by planting explosives, but as they were, Skynet grew at a geometic rate. John found them again and began attacking, taking Sarah hostage as a means to prevent the Guardian from activating the detonator. Unable to defy his programming to protect Sarah, the Guardian gave the detonator to Kyle and attacked John. A brutal fight ensued, in which the detonator was destroyed, but the Guardian managed to hold his own for a time, slashing John repeatedly with a laser post and seemingly making him incapable of taking on disguises anymore. However, John eventually gained the upper hand, ripping off the Guardian's left arm and threw him in front of a prototype time machine, helpless. John taunted him about his inability to defeat him, but Sarah and Kyle saved him.
With Skynet seemingly destroyed, they travelled to Kyle's childhood home where Kyle instructed his younger self to remember a message that would help them defeat Skynet. Watching Kyle interact with his younger self, the Guardian gave Sarah his approval in the form of admitting that Kyle is a good man. Believing they were free and have changed the future, Sarah and Kyle decided to make their own future together and kissed. When looked at for approval, the Guardian gave them his version of a smile and they drove off together.
- The Guardian, even before "taking the long way" between 1984 and 2017, is the oldest known active Terminator. It was in the past from 1973 to 1984 and aged accordingly while being shown to be about the same age as the previously shown members of its model in 1973. A Terminator surviving so long is apparently unheard of as Kyle said he'd never seen one so old before and didn't know that their skin sheath aged with them. In 2017, the Guardian was showing its age as well: along with having wrinkled skin and white hair, the Guardian was shown to be in somewhat of a state of disrepair as its servomotors would lock up at times, causing it to have trouble walking and its hand to be unable to grab. This may be due to lack of proper maintenance as a T-800's power cell is good for 120 years. Presumably these problems were fixed along with all the other damage the Guardian took when it bonded with the mimetic polyalloy.
- The Guardian was sent by an unknown party to protect Sarah in 1973. Whoever it is didn't want to be known so they took the precaution of erasing the Guardian's files on them. Sarah believes that this is because if she, Kyle and the Guardian didn't know, Skynet wouldn't find out either and couldn't target them. This indicates that they have an ally out there somewhere and has the resources to reprogram a Terminator, sending it through time.
- The Guardian proves more knowledgeable than the previously seen Terminators, such as having information on the T-3000 and how they were a failed experiment. He also seemed to have a great deal of knowledge of the original timeline and Kyle's part in it, information which he imparted to Sarah. Given that he and Sarah were able to build a crude time machine, this was likely from his knowledge database as well.
- The Guardian proves more adaptive than the other Terminators, possibly due to the longer time its been in the past and greater experiences with humans. Notably, it was crafty enough to help Sarah set up traps for its fellow T-800 and the T-1000, showing a knowledge of their weaknesses when the previous T-800 to face a T-1000 in the past didn't know how to permanently defeat it. Instead of declaring that as it was a superior model, he couldn't defeat the T-3000 like the T-850 did with the T-X, he came up with a way to fight and later destroyed him. Also, even without Sarah's guidance, the Guardian proved capable of blending in with humans enough to survive thirty-three years without suspicion and acquire a construction job for building the Cyberdyne building where Genisys was located.
- The Guardian seemed defensive of its age and the shape it was in, saying it was "old, not obsolete." When it has trouble holding bullets due to its failing parts, it repeats this to Kyle who finishes the sentence and seems to decide to keep it from Sarah.
- The Guardian is the only Terminator protector from the future in the films who survives the movie its in and the completion of its mission.
- Like the first T-800 in the original timeline and the protector one in Terminator 2, the Guardian lost his left arm. Unlike them, he managed to regrow it.
- The Guardian has terminated two major Terminator enemies in a film: the T-1000 and the T-3000.
- Several times in the movie, the Guardian attempted to appear more human by smiling, including when he got his mug shot taken. However, as Kyle pointed out — he just looked creepy instead.
- Seeing as John Connor had become the T-3000, Pops is the only Terminator that actually kills John Connor on screen.
- Guardian's outfit and look in 1973 is identical to the 1984 t-800s appearance during the West Highland Police Station shootout.