Originally Posted by
Johnny
The character's full name is John Thomas Diggle. He's never been called John Diggle Stewart. The Diggle name comes from Andy Diggle, who previously wrote Green Arrow: Year One, so the showrunners decided to honor him by naming one of their characters after him. On the show Diggle even has a younger brother literally called Andy Diggle because of that. Stewart is the last name of his stepfather that was never revealed until the last two seasons and he never officially takes that name. He's still John Diggle in the finale. His military background and being a black man with the name John was never intentionally meant to create associations with John Stewart, that became a fan theory that they eventually decided to acknowledge, no different than how Felicity became a main character on the show because people liked her when she was only supposed to be a guest character in the first season.