In Terminator: Genisys, the younger Sarah Connor's guardian Terminator is called Pops.
Pops is an older T-800 who has protected Sarah since childhood in the film’s altered timeline. His nickname reflects Sarah’s personal relationship with him rather than a standard Cyberdyne model designation.
The character is played by Arnold Schwarzenegger, whose T-800 portrayal is a recurring element across the franchise. Genisys changes the continuity by showing that Sarah’s history has already been altered before Kyle Reese arrives from the future.
Pops should not be confused with the original film’s unnamed killer Terminator or with the reprogrammed protector known informally as Uncle Bob in Terminator 2. Those characters are also played by Schwarzenegger, but the nickname belongs specifically to Genisys.