Here's how John Reese ended his journey on Person Of Interest. Person Of Interest is a grounded sci-fi thriller show from Jonathan Nolan that debuted in 2011. Prior to this series, Nolan was best known for working with his brother Christopher Nolan on several projects, including Memento, Interstellar and the screenplays for the final two instalments of the Dark Knight trilogy. Nolan also did uncredited work on Terminator: Salvation.
Jonathan Nolan is probably best known nowadays for HBO's Westworld. This series is a reboot of the cult 1973 thriller from Michael Crichton which is set in a futuristic theme park where visitors interact with lifelike robots; bad things happen when these androids malfunction. Westworld season 1 received praise for its performances and exploring the idea of these abused machines gaining sentience; Westworld season 3 will arrive in March 2020. Nolan explored similar themes with Person Of Interest, which focused on an A.I. that can predict crimes and becomes sentient. It's creator Finch (Michael Emerson, Saw) assembles a team to investigate its predictions.
At the start of Person Of Interest Finch recruits John Reese (Jim Caviezel, The Passion Of The Christ), an ex-CIA operative with a shady past, to look into the A.I.'s predictions. Reese is a highly skilled operative who keeps his emotions in line but is revealed to be haunted by the death of a loved one. He and Finch also form a friendship throughout Person Of Interest's five seasons, in addition to growing close to the rest of the team they assemble.
Person Of Interest season 5 was the final series and proved with some major deaths it was going out with a bang. This was never truer than its finale "return 0," which charts the efforts of Reese, Finch and The Machine to stop the Samaritan A.I. Samaritan is basically the evil version of The Machine, and after an attempt to destroy it with a virus fails when it uploads to a satellite, Finch realizes the only way to ensure its destruction is to upload The Machine to the satellite too. The Samaritan will launch a missile as a defense against such a move, so Finch locks Reese in a vault to keep him out of harm's way.
Finch later realizes The Machine has led him to the wrong roof for the upload, before noticing Reese in a building across the street. It turns out Reese and The Machine had a plan to keep Finch safe, with the former knowingly sacrificing himself to save his friend. John Reese's last moments on Person Of Interest sees him holding off gunmen attempting to stop his upload before he's overwhelmed and shot dead. The Machine made it to the satellite, however, destroying Samaritan before a missile destroys the building.
While it was a sad ending for Person Of Interest fans, Reese's exit was pretty much perfect. His sacrifice goes back to Finch giving him a renewed sense of purpose by recruiting him in the first place, and Reese died knowing he was stopping Samaritan whilst giving Finch a shot at a normal life with his fiancee. The ending also revealed The Machine survived it's apparent demise, meaning the A.I. will continue its crime-fighting ways.