An Irish citizen and nationalist, Doyle was a former Captain in the IRA who used the moniker "Valhalla". At some point of his life, he met Chloe Donaghy, with whom he fell in love with and had a son, named Declan. Chloe attempted to abort Declan before he was born by ingesting pills, but Doyle stopped her and imprisoned her until Declan was born with the help of his nanny Louise Thatcher. He then paid Chloe for giving birth to Declan and sent her on her way, unknowingly earning her wrath. His illegal activities with a breakaway faction of the army soon attracted the attention of Interpol, who considered him very dangerous. They assigned a team, codenamed JTF-12, to bring Doyle down, led by Clyde Easter and comprised of Emily Prentiss (who worked undercover as "Lauren Reynolds" at Doyle's private villa in Tuscany), Sean McCallister, Tsia Mosely, and her boyfriend Jeremy Wolff. The team arrested Doyle, but not before he figured out that Prentiss was working undercover to bring him down. Meanwhile, Prentiss engineered a plot to take Declan away from Doyle's life as a terrorist, staging his murder as well as that of Louise, now Declan's legal guardian, and sending photos of the faked murders to Doyle, which enraged him, as he had grown to love Declan. Doyle was later imprisoned at Camp 22, a North Korean political prison, for his crimes for seven years, where he swore revenge against those who destroyed his life and took away Declan. However, Prentiss assumed that he was in a Russian prison until McCallister told her that Doyle escaped from the political prison. While he was telling her, Doyle somehow traveled to Russia and hijacked a car there, stabbing the driver to death in the process.
Doyle makes his first appearance in a flashback, in which he witnesses Prentiss being taken away by Interpol as it closes in on him. He makes a phone call to an unknown receiver and says, "They got her." and says to stay on top of this. He is then arrested by two Interpol officials. At the end of the episode, Prentiss returns to her apartment to find that she has been sent a purple flower, a lilac Freesia, the same flower that grew at Doyle's old residence. Realizing it is a signal of his impending arrival, Prentiss hastily takes her belongings, including her cat Sergio, and clears out.
Deciding that it is time for his revenge to come, Doyle organizes the death of Jeremy Wolff, who was currently vacationing in Paris with Tsia, making it look like a stroke. Tsia finds out about Jeremy's death and calls Prentiss, who realizes Doyle organized everything and tells Tsia to dispose of her cell phone and leave Paris. At the end of the episode, Doyle is seen stepping out of the plane and getting inside a limousine, as the U.S. flag hangs from a wall in the background. It is later revealed in Coda that he got through security using the alias "Chuck Murray"; according to Clyde Easter, that was the name of an Irish Wolfhound Doyle owned before he went to prison.
Prentiss calls Clyde and Tsia to help her track Doyle down and kill him. After she calls them, Doyle meets up with Prentiss, who threatens him that she will shoot him in the crotch if he does anything to hurt her. Ignoring this threat, he tells her that he is there to take her life from her and that she will do as he tells her to do or he will kill everyone on her team at the BAU.
After his encounter with Prentiss, Doyle summons his gang, which killed the Cosenza family and Frank and Kerry Fagan, the Cosenza father, Ron, and Kerry Fagan being his handlers back at North Korea. After killing their victims, the gang made the Cosenza's family's deaths look like a murder-suicide, while Frank and Kerry Fagan's deaths were disguised as casualties from a house explosion from a gas leak. The BAU, unaware of Prentiss's connection with the unsub, realize that a man, Byron Delaney, is connected to Ron and Kerry, and Hotch sends Prentiss and Morgan to retrieve Delaney.
Prentiss and Morgan arrive too late, and they are forced to get into a gunfight with Doyle and his three present men after they murder Delaney. Eventually, Prentiss wounds one of the men and Doyle shoots and kills him so that he won't be able to be identified, even going as far as shooting his compatriot in the wrist, where a tattoo of their symbol is stamped on. This tactic fails, however, and as a result he ends up on everyone's list. This did not stop him though as he proceeds to kill Tsia, who is summoned to an address by Prentiss, who intends to meet up with her there. The address's current resident, a forger named Ben Corelli who had made fake IDs for Declan and his new legal guardian on Prentiss's behalf, is also killed. After this, he scopes Prentiss's house with Liam, another member who is apparently his lieutenant. When Liam states it would be easy to grab her, Doyle replies, "No."
It is revealed that Prentiss first encountered Doyle undercover as an arms dealer. They eventually developed a romantic relationship as exhibited when they kissed and Doyle gave Prentiss a necklace. Prentiss and Doyle had apparently grown so close that he asked her to take care of Declan, but she refused. Then, back in the present, Prentiss goes searching for Doyle. When she catches up to a couple of his soldiers, Ian takes two shots at her and takes her hostage. He then proceeds to brand her with a four-leaf clover and forces her to have Doyle's sniper kill Jack Fahey instead of her teammates.
Doyle then wants her to confess to involving his son in his life as a terrorist and wants her dead in revenge for his son's death, but Prentiss reveals that Declan is alive. She and Doyle then get into a fight, which ends with Doyle stabbing Prentiss in the abdomen, incapacitating her. When Doyle demands knowledge of where his son is, Prentiss, wanting to keep Declan away from his murderous father, refuses to disclose that information. In the end of the episode, when Doyle hears Morgan and the SWAT team shoot Liam and his men dead, he apparently makes a run for it and disappears. Prentiss's funeral is shown, but the last scene reveals she is in Paris, going into hiding from him.
Doyle is first seen being taken into custody by Morgan after assaulting the agent. They initially assume him to be responsible for the (non-fatal) poisoning of numerous children at Declan's school, the deaths of two FBI agents and Louise, and the abduction of Declan. However, he denies any knowledge of committing any of the crimes to Morgan, believing his accusations to be a ploy to get him to talk, and JJ realizes that Doyle is right. When Prentiss interrogates Doyle herself, Doyle decides to cooperate and identifies Chloe as Declan's mother.
Doyle later agrees to turn himself in to Chloe in order for Declan to be traded back to the BAU. Doyle agrees, and the BAU and local police arrive at the airport Chloe and an accomplice, Lachlan McDermott, are using to transport Declan out of the U.S. Lachlan, angered at Doyle for killing his brother, shoots a rebelling Chloe and takes Declan out of the plane, demanding that Doyle be handed over to him. However, Chloe, having survived a gunshot wound inflicted by McDermott, manages to walk out of the plane as well and shoots both Doyle and McDermott, killing the latter instantly. The BAU fire back, killing her. Doyle also dies from his gunshot, but not before he manages to hold onto Declan's hand when he states that he remembers him, and says, "Sorry, son."
Prior to his incarceration, Doyle attacked his known victims by stabbing. After his escape, he usually operated with his group, who killed most of his victims for him, but whenever he murdered personally, his weapon of choice was a suppressed semiautomatic .45 handgun. He also continued stabbing some of his victims. When he killed Samuel Cosenza, he executed him with a single gunshot to the head in front of his father as a reference to his initial belief that his own son was killed in the same manner. In addition, Doyle killed Byron Delaney by injecting poison into his system as means of making his death look like natural causes.
Not much specific details of Doyle's original profile made by JTF-12 is disclosed, other than he is organized, meticulous, and very driven. In Valhalla, having spent years in a "hellhole" of a prison, he is driven by a need for revenge and will not let anyone stand in his way, even getting the child of one of his handlers killed in spite of his innocence. It was also mentioned that he is extravagant, though the only sign of extravagance in his life seen on the show was his mansion in Italy. Clyde Easter described him as a power-assertive psychopath who is serious about what he does and "doesn't play games". He becomes very explosive when his plans go wrong.
Prentiss: I knew you were watching me.
Doyle: What's the expression? Keep your friends close, your enemies under surveillance.
Prentiss: I've been here for two hours. You should know better than to keep a lady waiting.
Doyle: Seems hypocritical, seeing as I had to wait seven years.
Prentiss: Hello, Ian.
Doyle: Hello, Lauren. Oh wait, Lauren Reynolds died in a car accident, didn't she?
Prentiss: What do you want?
Doyle: You. Oh, not today, don't worry about that. But soon.
Prentiss: I've got a Glock leveled at your crotch. What's to stop me from taking you and the little ones out, right now?
Doyle: You'd never make it back to your car, and you know it. Tell me, does the lovely Penelope know the truth about you? Or is she too busy watching movies with Derek to care? Here you are, all alone, while Aaron sits at home with his son. And why didn't Dave and Ashley invite you to their game night? Maybe they thought you'd be on the Metro with Dr. Reid. (laughs) Well, that one does have some quirks.
Prentiss: Come near my team, and I will end you.
Doyle: I don't have a quarrel with them. How long that remains the case, depends entirely on you. They're innocent, you're not.
Prentiss: I was doing my job.
Doyle: I think you did a little more than that. You took the only thing that mattered to me, so I'm going to take the only thing that matters to you: your life. (puts a matchbook with a four leaf clover on it on the table between them) Honore de Balzac once said, 'Most people of action are inclined to fatalism and most of thought believe in providence.' Tell me, Emily Prentiss, which do you think you are gonna be?
Doyle: (referring to Declan) Happy birthday, my love.
Doyle: (to Prentiss while holding a gun at her) Hello, love.
Doyle: (to Prentiss, smiling): Hello, Lauren. Good to see you again.
Doyle: (to Morgan) Gonna kill me yourself, Agent?
Declan: I remember you.
Doyle: Sorry, son.
- Timothy V. Murphy, the actor who plays Doyle, also portrayed an international criminal in the CBS police procedural NCIS: Los Angeles. On Sons of Anarchy, he also portrayed an IRA member.
- In 52 Pickup, there appears to be some foreshadowing related to Doyle being offered; Prentiss mentions to Hotch that she has "actually dated men worse than Viper".
- Season Six
- Season Seven
- Season Eight
- The Replicator (referenced)
- Season Nine
- 200 (mentioned)
- Season Eleven