from Criminal Minds says that he knew Cooper for twenty years. It is also quite clear that he and Aaron Hotchner, also from Criminal Minds, have a past as well, but the matter remains moot.
Criminal Minds
In the episode "The Fight", he calls Hotch to come to Washington, D.C. to discuss with him about a case that seems related to a disappearance of a father and a daughter, saying that he has a theory. When Hotch asks him why he is going by Strauss' orders not to work on the case with Hotch's team, Cooper says that they are missing and no one is looking for them. As Hotch's team worked with the SFPD, Cooper and his team worked in a warehouse, and sometimes Hotch's teammembers would pop in once in a while for more clues. He even goes with Hotch to interview the wife of the missing husband and his daughter. When Erin Strauss called Hotch about the status of the investigation, Cooper asked for the phone. Cooper then starts negotiating with her about staying in San Francisco and solving the case, at which she eventually tells him, "Tell Agent Hotchner that I will deal with the two of you when you get back." With the help of Garcia, who also works with his team, they were able to identify the killer. When they get to the abandoned warehouse that the killer was in, the girl is gone and the father tells him that he took her and Cooper promises that he will find her and goes into a chopper and finds the killer and the daughter. When the killer was surrounded, he tells the pilot not to "blind his agents" as they are negotiating him to let the daughter go. When it appeared that the killer jumped off, Prentiss checks to see if he died. But the killer was still alive and was about to kill Prentiss, then shots came from Rawson, who is a sniper. Cooper then smiles, now that he knows that Prentiss is safe and that Rawson saved her life. When his team and Hotch's team were celebrating the closure of the case, Strauss calls him, telling him to get on the plane with Hotch and his team, saying that she has a pile of cases for him.
In the show, Cooper appears to be a gifted profiler like Jason Gideon, as seen in "See No Evil". He also is shown to be more cautious and concerned for his team members, especially Mick Rawson and Gina LaSalle. In the episode "Death By a Thousand Cuts", Beth Griffith is kidnapped by the unsub and Cooper had to make a choice whether to sacrifice Beth or risk his career by killing the unsub's son. The episode ends with a cliffhanger and Beth's fate remains compromised.
