John Greer is the alias of a former MI6 agent working for Decima Technologies, a shadowy organization that appears to be based in China, and is conducting cyber warfare. His purpose seems to be to serve Samaritan and to destroy the Machine in order to let the world be ruled by Samaritan.
Greer was raised in London, from which he was evacuated as a young boy during the Blitz. His early experiences with the war would shape his later life profoundly and made his will to become an MI-6 operative.
By the mid-70s, Greer was a field officer with the British Secret Intelligence Service (MI-6). In 1973 Greer was given an order by his superior at MI-6, Blackwood, to kill a Russian spy in London named Oleg Luski. While trying to capture Luski, Greer’s partner, Jacob, is shot and killed. Greer wounds Luski and later interrogates him to discover that Blackwood is a KGB double agent who ordered Luski’s death to cover up his own involvement. Disillusioned by this betrayal, Greer kills Blackwood before telling him that political boundaries have no meaning now and that one day all boundaries will be erased and there would be no need for an organization like MI-6. He then destroys his own dossier and disappears (“The Cold War”).
Early Activities with Decima
Greer re-emerges in 2010, now working for a shadowy organization using the cover name Decima Technologies. Decima targets Daniel Casey, a programmer nearly killed by the government for learning secrets about the Machine. A Decima operative named Lambert unsuccessfully tries multiple times to recover Casey following a failed meeting, and later meets with Greer at an alleyway. Greer gives Lambert the task of retrieving Casey's laptop and warns that he will find someone else to do his job, implying that he will have him killed, if he fails.
Acquiring the Machine
Greer visits Kara Stanton at an unknown hospital in Dongsheng (“Dead Reckoning”), China after she is injured in the Ordos mission (“Matsya Nyaya”). Stanton assumes he works for China's Ministry of State Security (MSS), but he responds by joking about his tailor, indicating he has other, more things to offer her. He tells her that she's in a sort of post-CIA "afterlife" before teasing her with the laptop in an attempt to fuel her desire for revenge. It's clear Greer wants Kara to execute an operation.
On a subsequent visit, Greer attempts to connect with Stanton by discussing how the people she worked for betrayed her. He uses her study of the classics, and the mythical Titans as an analogy to manipulate and brainwash her to ask the one question on her mind: who was behind the attempt on her life. He offers her the chance to operate for him and his organization, and in return will give her the name of the person truly responsible for her mission in Ordos, who sold the laptop in the first place (“Dead Reckoning”).
Having planted the virus in the Department of Defense computers, Stanton calls Greer at the end of the mission. Greer confirms that the malware is spreading through its target network and Kara demands to know who betrayed her. Greer tells her that a name is all that he has for her because the person doesn't exist in any known database. He gives her an unheard name, which she writes down. After the car explodes, a burned piece of paper with Harold Finch written on it sits in the wreckage (“Dead Reckoning”).
After Martin Baxter and Rylatech are exposed, he calls Baxter and convinces him to kill himself to cover Decima's involvement. Now in New York, Greer, on a cell phone, talks to an unknown second person about the impact of the fall of Rylatech. He offers assurances that the U.S. government is focused on China, but unaware of his group's other activities. Greer reports that the breach of their network was the work of one person, who he will "render irrelevant", but that their larger project is on schedule.
As he does, Finch and Reese discuss Finch's tracing of code Finch saw while at Rylatech to a company called Decima Technologies, named for one of the mythological Fates who control the thread of life. Finch believes that Decima has developed the virus Stanton uploaded with one purpose: to infect The Machine.= (“Trojan Horse”).
Shortly before the Decima virus counts down to midnight, Greer meets Reese and Sameen Shaw at the Thornhill offices. He explains that he knows everything about them before refusing to stop the virus, since he is invested in the outcome. However, he describes that Harold Finch created the virus, not Decima, but was not able to modify it's code without accessing the Ordos laptop first . He then reveals the name of the man that sold the laptop and the one responsible for all "this" to Reese: Harold Finch, suggesting Reese to tell Finch that Greer is looking forward into meeting him in the future (“Zero Day”).
Search for Samaritan
After Decima fails to gain access to the machine, Greer turn his attention to a second machine developed by Finch's old classmate at MIT, Arthur Claypool. One of Decima's operatives is able to infiltrate the bank vault holding the Samaritan drives and later brings them to Greer. He thanks her before shooting her dead to cover his tracks, and he plans to use Samaritan for Decima's own needs (“Aletheia”).
Greer and Decima target Cyrus Wells, a former millionaire turned janitor who has retinal access to a room belonging to a company called Maxwell Limited - the room stores a processor chip of sufficient speed to run Samaritan. Greer and Decima arrive for Cyrus at the same time the organization Vigilance attacks, and Cyrus is saved.
Decima operatives later ambush Cyrus and Root in Central Park, and despite Reese's efforts to stop them, Cyrus is kidnapped.
After Cyrus' eye is used to bypass a retinal scanner in the room, Greer orders Cyrus killed - Reese and Fusco arrive to save him. Root arrives, and in the ensuing gunfight, rescues Cyrus. The Decima operatives still take the chip and on Greer's orders burn up their computers with gasoline to eliminate any evidence (“Root Path (/)”).
Greer later hires Ken Davis, the corrupt CEO of energy company HydralCorp, to request the shipment of six generators to the USA, thus derailing their original shipment to Iraq. At a subway terminal, Root follows Greer through a hallway, and Greer, knowing he is being followed, uses voice commands to tell Samaritan to employ counter-surveillance tactics. He places his phone in the pocket of a man resembling himself and disappears. Root later uses Bear to follow Greer. She watches him meet with Davis, who reports that the generators have been delivered. Greer compliments Davis for his work and then has his men place a black hood over his head and take him off presumably to be killed. Root follows Greer through the same subway terminal and this time uses Bear's searching skills to sniff out Greer, resisting his counter-surveillance measures. Greer meets her in a vacant hallway and commends her for her tracking skills. He says that it's human nature to control things and information is the new currency, offering Root a position on Decima. Root wonders why he's negotiating, and two men aim their guns at Root. Greer declares their meeting a draw and walks away, allowing her to leave (“Allegiance”).
In Washington D.C, Greer meets with senator Ross Garrison in front of Hieronymus Bosch’s triptych The Garden of Earthly Delights. They discuss how the machine failed to protect itself from Vigilance and how Greer can help the country. Greer tells the senator that he has an alternative to the machine and proposes to green-light the program. At a later time at the same location, Greer asks Garrison if he will help him or not. He then tells him that if Samaritan has access to the government feeds, it will find a terrorist for him. After Samaritan receives the government feeds by Ross Garrison, Greer meets with Virgil in an unknown location, telling him to find Harold Finch (“Death Benefit”).
At a later meeting Greer tells Garrison that in the time Samaritan has been active, Samaritan has found many possible targets and assures that a terrorist will be found soon. Virgil tells Greer that Samaritan cannot find Harold Finch but says that he could search the name for any connections. After Samaritan finishes the search, Greer tells Virgil to bring Grace Hendricks to him. After a failed attempt from a Decima operative to abduct Grace, Greer tells Zachary to find Grace and kill Reese and Shaw. He then tells Virgil to tell their men to position themselves wheres there is no surveillance coverage as the machine can see them. After Grace is kidnapped, Greer interrogates her, then finds out that she was engaged with Finch four years ago. Shortly after Reese and Shaw arrive at the location, seizing Virgil but not finding Grace, Greer shows up on a screen telling them that Virgil cannot be questioned, which prompts him to kill himself. He then tells them that he will be willing to return Grace in exchange for Finch. Finch hands himself over to Greer in place of Grace and is taken to an abandoned building, where Greer finally meets him and tells him that he has been a very hard man to find (“Beta”).
In the building, Greer discusses with Finch about The Machine and Samaritan and how Finch damaged the machine. Finch tells him that he can never understand and that it is hubris to think he could control Samaritan. After a blackout that affects the city, Greer is reminded of his youth and talks about The Blitz. He then tells him that he wants to live under a more just rule by bringing Samaritan online. He meets Senator Garrison and tells him how Decima will retain ownership of Samaritan, Garrison challenges Greer's proposal but he says that it is his terms. Greer's hideout is breached by Peter Collier and other Vigilance members and everyone is taken captive. Greer is held alongside Sen. Garrison, Finch, Control and Manuel Rivera in a Kangaroo court (“A House Divided”)
As Collier prepares to execute them for crimes against the people of America, Lambert and his team break into the courthouse and execute the Vigilance members and wound Collier. Greer then reveals that he created Vigilance, and that it was he who was controlling Collier without his knowledge. He has the rest of the Vigilance members and other witnesses killed in an explosion in the court house and later has Lambert execute Collier. Finch is rescued by Reese but Greer uses the explosion at the courthouse to trick Garrison into giving him unlimited access to NSA surveillance feeds so that Samaritan may be able protect the nation against such "terrorist acts". After gaining access to the feeds Greer order the death of all remaining Vigilance members as well Reese, Finch, Shaw and Root, forcing them to go into hiding. As Samaritan fully comes online, Greer voluntarily relinquishes his command to Samaritan and waits for its instructions (“Deus Ex Machina”).
The New Regime (2015)
After Samaritan comes online Decima Technologies is dismantled as a viable business entity with Greer reporting only to Samaritan. He meets with Sen. Garrison and discusses the effectiveness of Samaritan's methods. After Garrison questions Greer's accountability he proposes if the senator should be eliminated but Samaritan disagrees (“Panopticon”).
After Samaritan becomes interested in Elizabeth Bridges' algorithms it has one of its representatives invest in her company. Greer remains unsure of what Samaritan sees in Elizabeth's algorithms (“Pretenders”).
Though Samaritan is unable to deduce Shaw's identity Greer figures out she is working with Finch and is somehow hiding in plain sight (“Point of Origin”).
After Greer discovers that the machine is blocking all relevant data about Finch and his associates, he proposes to bypass it by relying on human intelligence and expands Martine's capabilities by providing her with a team to hunt down Shaw (“The Devil You Know”).
Greer oversees Samaritan's operatives including Lambert and Martine as it takes over New York for a day to force the Machine out of hiding. He later informs Lambert of Samaritan's plan to launch a cyber-attack on the stock exchange for the whole world to see (“The Cold War”).
Reese, Finch , Root and Fusco infiltrate the basement of the stock exchange and try to install a software in the exchange's servers to prevent further market collapse. Even without any surveillance Greer once again oversees Lambert and Martine and guides them as they hunt for Finch and his team (“If-Then-Else”).
Following a conflict between Control and Travers, one of Samaritan’s representatives, regarding Samaritan’s intel about a terrorist attack, Greer calls Sen. Garrison and reminds him of their previous arrangement which prompts him to force Control to back down (“Control-Alt-Delete”).
Greer is present alongside Shaw when she wakes up at one of Samaritan’s facilities, he tells her to get some rest because she is going to need it soon (“M.I.A.”).
Greer sends Claire Mahoney to lure Finch out of hiding and bring him over to their side. She nearly succeeds but Root rescues Finch and wounds Claire even as she manages to escape. Greer praises Claire for her commitment to Samaritan's cause and explains that if she had died on the mission it would have been for a good cause. He later meets Lauren Buchanan, the CEO of Fetch and Retrieve, to acquire their company (“Q&A”).
After Samaritan hacks into the software developed by businessman Sulaiman Khan to look for the Machine, Khan is captured and taken to Greer, who confirms the existence of both the Machine and Samaritan. Khan demands to "look in [Samaritan's] eyes", prompting Greer to shoot him dead and leave his corpse looking at Samaritan's emblem on the computer screen (“Search and Destroy”).
While infiltrating Samaritan's headquarters Root and Finch are captured by Martine and her agents and brought to Greer for questioning. When Root kills Martine by snapping her neck Greer nonchalantly has her body removed from the scene much to Finch's surprise. After the Machine gives up its location to Samaritan in exchange for Root and Finch, Greer sends an army of his agents after it (“Asylum”).
Control tracks down Greer and holds him at gunpoint to question him about "The Correction". Control figures The Correction is an attack on the Supreme Court but Greer proves to be one step ahead of her and states that The Correction is actually a list compiled by Samaritan comprising criminals, disruptive outliers and disloyal people to be eliminated at the right time. As the subsequent deaths flash on a screen before them, Greer tells Control that this was a test of loyalty which she has failed and that she will be taken to a place she deserves. She is then captured by Samaritan agents and taken away as Greer continues to watch The Correction taking place all over the world (“YHWH”).
Greer is later seen ordering experiments on Shaw, plunging her brain into virtual realities to reveal the whereabouts of the Machine and the Team, and forcing her to kill her friends. In the 6741st test, Shaw kills Greer and Reese but keeps never killing Root, making suicide thus terminating the simulation without having revealed anything about the team. Greer remains stoic, saying "We have all the time in the world", plunging Shaw back into more simulations until a potential result (“6,741”).
After more than 7000 tests and failures, Greer tries a different kind of simulation to recruit Shaw within Samaritan's assets. He seemingly takes her in the outside world for a walk to show her how Samaritan would radically prevent murders, bombings and other atrocities way before the Machine would even warn her team of the existence of a threat. The simulation ends up with Gabriel Hayward making up an apocalyptic vision of a third world war, without Samaritan's actions to protect mankind. Greer then greets an awoken Shaw (“A More Perfect Union”).
As Finch infiltrates Fort Meade to destroy Samaritan with the ICE-9 virus, the Machine gives Reese and Shaw a new number, Philip Hayes, the alias Greer used at the Office of Intergovernmental Studies. After uploading the virus but before he can unleash it, Finch is apprehended and brought before Greer who reveals that Samaritan wants to rule the world alongside the Machine. Finch refuses to cooperate, but in doing so, reveals that the Machine lacks knowledge of the password that would unleash the virus. Greer then locks himself and Finch in sealed room and has the air sucked out, planning on sacrificing himself to kill Finch and protect Samaritan. Greer dies of suffocation from lack of oxygen, but Finch survives long enough for Reese and Shaw to enable the Machine to rescue him. Finch later tells them of Greer's death in a failed attempt to kill him (“.exe”).
- Presumably killed numerous people under the employ of MI-6.
- Oleg Luski: Shot and tortured; allowed to escape (“The Cold War”).
- Blackwood: Greer's boss at MI6 who's a double agent with the KGB, shot and killed (“The Cold War”).
- Daniel Casey: Targeted under his orders; survived (“RAM”).
- The employees at the Ordos facility: Killed on his orders (“Matsya Nyaya”) (“RAM”).
- Monica Jacobs: Targeted to protect Rylatech's involvement with Decima; survived (“Trojan Horse”).
- Martin Baxter: Forced to commit suicide by Greer to protect Decima's involvement (“Trojan Horse”).
- Jerome Eckert: Killed by a Decima sniper to protect their anonymity (“Trojan Horse”).
- Bank Manager: Shot by Greer to cover his trail (“Aletheia”).
- Cyrus Wells: Kidnapped and targeted on Greer's orders; survived (“Root Path (/)”).
- Ken Davis: Knocked out and presumably killed by Greer's men to cover his trail (“Allegiance”).
- Grace Hendricks: Targeted and kidnapped on Greer's orders; survived (“Beta”).
- Virgil: Killed himself on Greer's orders (“Beta”).
- The crew of the cargo ship containing the Samaritan drives: Poisoned to death to cover Decima's involvement (“Beta”).
- Harold Finch: Kidnapped (“Beta”) and later shot by Lambert on Greer's orders; survived (“Deus Ex Machina”).
- Peter Collier: Shot and killed by Lambert on Greer's orders (“Deus Ex Machina”).
- Steven E. Soto: Shot and killed by Lambert on Greer's orders (“Deus Ex Machina”).
- Jefferson: Shot and killed by NYPD officers under Greer's manipulation (“Deus Ex Machina”).
- A number of Vigilance members, NYPD officers, journalists and civilians were killed in the post office explosion carried out on Greer's orders (“Deus Ex Machina”)
- Novak: Shot and killed by Martine on his and Samaritan's orders (“Panopticon”).
- Simon Lee: Targeted under his and Samaritan's orders; survived (“Prophets”).
- Sameen Shaw: Shot and kidnapped on his and Samaritan's orders (“If-Then-Else”).
- Sulaiman Khan: Shot and killed by Greer (“Search and Destroy”).
- Schiffmann: Killed by a Samaritan operative on Greer and Samaritan's orders as part of The Correction (“YHWH”).
- Devon Grice: Shot and killed by a Samaritan operative on Greer and Samaritan's orders as part of The Correction (“YHWH”).
- Dominic: Shot and killed by a Samaritan sniper on Greer and Samaritan's orders as part of The Correction (“YHWH”).
- Elias: Shot by a Samaritan sniper on Greer and Samaritan's orders as part of The Correction (“YHWH”).
- Control: Captured and imprisoned by Samaritan agents on Greer and Samaritan's orders as part of The Correction (“YHWH”).
- A number of criminals, disruptive outliers and dissidents killed under Greer and Samaritan's orders as part of The Correction (“YHWH”).
- Harold Finch: Locked in a room with Greer and the air evacuated to kill Finch. However, Reese and Shaw enable the Machine to rescue Finch before he succumbs (“.exe”).
- Himself: In an attempt to kill Harold Finch, Greer traps the two men in a room and has the air evacuated. Greer suffocates to death as a result (“.exe”).
Note: The virus that was uploaded by Kara Stanton on Greer's orders affected The Machine in such a way that it failed to send the numbers of potential victims on time to Finch and led to the deaths of Alan Fahey, Cal Beecher, Bill Szymanski and Dr. Richard Nelson.
- At Panopticon and Point Of Origin, Greer is labeled as ADMIN, by Samaritan. However, in The Cold War and all episosdes after it, he is labeled as PRIMARY ASSET.
- Greer is the most frequently appearing recurring character on the show, having appeared in 28 episodes.
- In “Zero Day”, we can see that the car Greer rides in is assigned a white square. It is unclear whether he still does not know about the Machine or if the box is assigned to one of the Decima operatives in the car.
- In the flashbacks in “Dead Reckoning”, the Machine has assigned Greer and Stanton white boxes, indicating they do not represent threats to it. By the events of “Trojan Horse”, the Machine has assigned a red box to Greer, indicating he now poses a threat to the Machine.
- In “RAM”, Greer's name is mentioned for the first time. The machine displays his name as "[REDACTED]" suggesting that it might be an alias. The alias is confirmed in the opening sequence of “Root Path (/)” and his title with Decima is listed as "Director, Operations". In “Dead Reckoning”, while talking to Stanton, Greer says, "My employers have an inkling of what happens next." It remains unknown who these employers are.
- Greer appears to be from London, England as he told Finch about experiencing German air raids when he was a child, which mainly targeted London, and that he sought shelter in the London Tube network (underground railway) (“A House Divided”).
- In the episode “The Cold War”, it is hinted Greer's first name initial to be "M"
- During their final encounter, Finch tells Greer that he's gone insane given his beliefs in Samaritan as a digital god. (“.exe”)
- Greer is the most frequently appearing recurring character on the show. His first appearance was in the thirteenth episode of the second season. His last appearance was in the twelfth episode of the fifth season. He has appeared in 28 episodes.
- John Nolan, who plays Greer, is the uncle of showrunner Jonathan Nolan and his brother, film director Christopher Nolan.
- “Root Path (/)”
- “Death Benefit”
- “A House Divided”
- “Deus Ex Machina”
- “Point of Origin”
- “The Devil You Know”
- “The Cold War”
- “Search and Destroy”