John Diggle was created for the TV series "Arrow", where he is Green Arrow's sort-of sidekick. He's also his bodyguard, who was hired by Moira Queen. His last name of "Diggle" is named after Green Arrow: Year One writer Andy Diggle. The character proved to be so popular that Green Arrow writer Jeff Lemire introduced him into the DC Universe proper in Green Arrow #24.
Major Story Arcs
When the Zero Year crisis happens, Moira Queen, Oliver Queens mother, comes to Gotham to help, and John Diggle is one of her personal bodyguards. Killer Moth found out she was in the city and attempted to kidnap her, he knocked out Moira's other guard but Diggle was able to hold him off until backup arrived in the form of Batman followed shortly by Green Arrow, he then made sure Moira was safe. After the fighting Moira decided to go with Arrow instead of Batman, then revealing she knew he was her son in front of Diggle.
One month after meeting in Gotham, Green Arrow come to Diggle for help after a near death experience. After saving Olivers life he's offered a partnership, since Ollie knew Diggle could be trusted as he didn't tell anyone, he knew he had a military background. Oliver could see that while not working Diggle had a drinking problem and needed something more, and while he never wore a mask and used a gun, he stopped crime with Ollie and even with Roy Harper.
The Outsiders War
John Diggle met with William Tockman, proposing a deal in order to stop Richard Dragon before he take over all of Seattle, he also met Henry Fyff and Naomi Singh and they agreed to help. While having a meeting, Tockman betrays Diggle saying Dragon offered him a better deal, and Diggle ends up in Dragons hands while they let Fyff and Naomi go, to let Green Arrow know.
While captured by Dragon, he's beaten and eventually learns Dragons origin, and reveals how it wasn't the Green Arrow, but himself, who humiliated Dragons father and inspired him to train like he did. When Oliver Queen returns to Seattle, he's informed of Diggles situation and comes to his rescue. After saving Diggle from a fall, Ollie and Dig go back upstairs to deal with Dragon and all him men, and while neither are able to beat him, together they pull off a desperation move that successfully stops Dragon.
While Naomi and Fyff heal, and Emiko trains, Diggle stays with Ollie, helping him both in the field, and occasionally over the radio from their main base.
Powers and Abilities
While he doesn't have any superpowers, he is a well trained Green Beret, and trained with Oliver Queen and Roy Harper for an unspecified amount of time.
He is a marksman and was fast enough to shoot 2 men before they could shoot Oliver at close range, Richard Dragon also noted that he is ambidextrous.
The New 52: Futures End
In the potential future of Futures End, which takes place five years into the future of the current DC universe, Diggle is still considered a close friend and ally of Oliver Queen, the Green Arrow. After Queen is "killed" in action, Diggle is seen as one of the pallbearers at his funeral. When Oliver makes his return Diggle is with him and helps with the attack on CADMUS Island.
Diggle first appeared in the Pilot episode as Oliver's bodyguard and chauffeur after he had been kidnapped. He's shown in the show as being very logical keeping his emotions out of his decisions most of the time though he on one occasion left his emotions in and it almost cost him Carly's life.
He has a vendetta against Deadshot who killed his brother and has threatened to kill him. Diggle is more than willing to leave the team as shown in the episode Home Invasion if that is the only way to fix the problems and he only came back in the episode Lone Gunman when Oliver apologized about everything.
He's shown to care deeply for Oliver and he always is seen doing what is best for him even if it means it will hurt him in the now. He's also the first person in the series to ever find out who the Hood identity.