Red

Frank Moses, retired black-ops CIA agent, lives alone in Cleveland, Ohio. Lonely, Frank often chats on the phone with Sarah Ross, a worker at the General Services Administration's Pension Office in Kansas City, Missouri. He creates opportunities to talk to her by tearing up his pension checks and calling her to say they had never arrived.
One night, a wetwork squad raids Frank's house and attempts to kill him, but he easily wipes them out. Knowing they have tapped his phone, he believes Sarah will be targeted. In Kansas City, as Sarah refuses to go with him, he forcibly ties her up and gags her with duct tape. Meanwhile, CIA agent William Cooper is assigned by his boss, Cynthia Wilkes, to hunt down and kill Frank.
To find out who is targeting him, Frank tracks down his old associates for help. He goes to New Orleans, Louisiana and visits his C.I.A. mentor, Joe Matheson, who now lives in a nursing home. Joe tells Frank that the same hit squad murdered a reporter for The New York Times. Locked in a motel by Frank, Sarah escapes. Another agent, posing as a police officer, tries to kidnap her, but Frank returns in time. Cooper attacks them, but Frank tricks the police into arresting Cooper and escapes with Sarah. The two head to New York City and find clues left behind by the deceased reporter, which leads them to a hit list.
They then find Marvin Boggs, another former black ops agent and a paranoid conspiracy theorist. Marvin tells them the people on the list, including Frank and Marvin, are connected to a 1981 secret mission in Guatemala. Another person on the list, Gabriel Singer, is still alive. The trio tracks down Singer, who tells them that the mission involved extracting a person from a village. Singer is then assassinated by a helicopter-borne machine-gunner, and the team escapes as Cooper closes in.
Frank goes to ex-Russian secret agent Ivan Simanov, who helps him infiltrate CIA headquarters. In the CIA archive, the records keeper, who has much respect for Frank, simply hands him the Guatemala file. Frank confronts Cooper in his office and the two have a vicious fight. Though victorious, Frank is shot during his escape. Having escaped an attempt on his life, Joe arrives and helps extract the team. They hide out in the home of former wetwork agent Victoria (Helen Mirren), who treats Frank's wound and joins the team.
The file gives them clue to the next lead, Alexander Dunning, an illegal arms dealer. Frank, Marvin and Joe enter Dunning's mansion, with Joe posing as a buyer, while Victoria and Sarah keep watch outside. They interrogate Dunning, who reveals the target for extraction was the nowâVice President Robert Stanton (Julian McMahon). Stanton ordered the hit on the people involved in the mission to hide the fact that he massacred village civilians.
Cooper and the FBI surround Dunning's mansion. Cooper tries to negotiate Frank's surrender, and Frank tells him about the Vice President's treachery. The terminally ill Joe pretends to be Frank, walks outside, and is killed by an unknown sniper. The confusion, as well as Victoria's cover fire, buys the team enough time to leave the mansion, but Sarah is captured. They escape with the help of Ivan, who is Victoria's old flame. Frank calls Cooper from his family's phone and warns him against harming Sarah.
The team, along with Ivan, kidnaps Stanton. Frank calls Cooper, offering to trade Stanton for Sarah. At the meeting point, Dunning arrives. After a short dialogue, Dunning injures Stanton, revealing himself and Cynthia Wilkes to be masterminds behind the assassinations. Disgusted with Wilkes' corruption, Cooper pretends to arrest Frank, but shoots Wilkes. Marvin and Victoria kill Dunning's bodyguards, and Frank kills Dunning by crushing his windpipe. Cooper lets Frank's team go. As they leave the scene, Frank and Sarah are eager to start a new life together.
Ivan reminds Frank of his favor. A few months later, Frank and Marvin are in Moldova with a stolen nuclear device. They flee from Moldovan Army troops with Marvin wearing a dress and in a wooden wheelbarrow being pushed by Frank.

Question: Who is Frank's C.I.A. Mentor?
Answer: Joe Matheson