"Arrow" star Stephen Amell, recently asked about the return of actor Colton Hayes to the show as crime-fighting, 'Roy Harper', aka vigilante archer 'Arsenal', replied, "..if we end this show, whenever it happens to end, without seeing 'Roy Harper' again, I think we will have made a tragic mistake...":
'Roy' first appeared in the season one "Arrow" episode 'Dodger' as a thief who steals the purse of 'Thea Queen'.
Eventually they reconcile and start dating, though their relationship is on and off. After 'Oliver' saves Roy's life in "Salvation", he gains an active interest in the vigilante known as the 'Hood' and wants to emulate him. Roy continues to act as a recurring character throughout the rest of the season and becomes a series regular starting in season 2.
In season 2, Roy fights crime in acts of vigilantism like the Arrow before he is captured and injected with the super-soldier drug 'Mirakuru', enhancing his physical capabilities...
...giving him superhuman strength and healing, able to punch through solid wood and recover from being shot at point-blank range- but also causing his behavior to become hostile and violent.
Oliver approaches Roy as the Arrow and offers to train him to help him learn to control both his physical and mental performances and to keep those around him safe. Eventually Roy learns the Arrow's identity and officially joins 'Team Arrow'. In the episode "Birds of Prey", Oliver calls Roy his sister's nickname 'Speedy'. Roy is not too pleased by this and tells Oliver not to call him that.
By the end of season two, Roy is cured of the Mirakuru and Oliver gives him a red domino mask. Roy chooses to fight by Oliver's side to save the city from the army of 'Slade Wilson', hoping to achieve redemption, but at the cost of his relationship with Thea.
Roy assumes the name 'Arsenal', in a red version of Oliver's costume and equipment. This came to fruition in the premiere of Season 3 of "Arrow", when Roy dons a red suit similar to Oliver's and with his own red arrows. In the Season 3 episode "Guilty", Oliver suggests the name 'Arsenal' after the antagonist of the episode refers to him as 'another weapon in Oliver's arsenal'.
Click the images to enlarge. and Sneak Peek 'Arsenal'...