|“||And I'll carry that with me till the day I die! Until that day comes I'm gonna be a very, very wealthy man...||„|
|~ Walker to Diggle|
Colonel Walker is a villain in the fifth season of Arrow and acts as an antagonist to John Diggle. Walker is portrayed by Garry Chalk.
In a military briefing, Colonel Walker informs a team that a military trigger, remaining from one of the nukes that fell at Genesis Day, is about to be obtained by Chechen rebels. Calling it a standard retreival and extraction mission, Walker gives Diggle command of the mission.
During the mission, Diggle and his men are able to defeat the terrorists. After Diggle has tended to the wounds of one of his men, the two separate and try to sweep the corridors. While doing so, Diggle hears the voice of Walker and, believing him to be an ally, reveals himself to Walker. However, Walker's men disarm Diggle and Walker reveals that he has not come to secure, but to sell the trigger. Diggle calls it theft but Walker replies that you can't steal what nobody owns. He also warns Diggle to remain quiet, claiming that Diggle might just live through the situation should he remain calm.
While Walker and his men are waiting for their contacts, Walker sends two of his men to check the roof. When the two are gone, Diggle angrily accuses Walker of having murdered his own soldiers by having them walk into an ambush. Walker replies that he will carry that burden with him to the day he dies, but that he will be a wealthy man until that day comes. When Diggle reminds Walker of the oath he has sworn to his country, Walker angrily replies that, while he was able to take on enemies like Al-Quaida and the Taliban, he sees no chance of defeating meta-humans and users of magic.
Walker's men soon return, having captured Diggle's remaining teammate. Walker shoots the man with Diggle's gun. He tells Diggle that he realises that his contacts will never show up, as Diggle must have killed them before. He claims that Diggle's presence will nonetheless prove to be useful and knocks out Diggle. Diggle regains consciousness on the military base, where Walker is standing next to him. Walker hands the cuffed Diggle a paper, revealing that it is supposed to be Diggle's confession. Diggle spits on the confession and Walker urges him to reconsider, claiming that he shot the private with Diggle's gun and that he will turn the story so that Diggle turns out to be the one who tried to illegally obtain and sell the trigger. Walker also claims that his corrupt soldiers will also testify against Walker.
Diggle is imprisoned in a military prison. Although nearly everyone urges him to, Diggle refuses to fight, claiming that he deserves to be put away for murdering his brother Andy. Oliver later breaks him out and Diggle goes into hiding. However, Walker manages to lure him out, faking a call from Diggle's wife Lyla claiming that their son is sick. Once Diggle rushes home, he is awaited by Walker's men and captured again.