The Queens mansion exterior shots are filmed at the same castle they used to use as Luthor's castle onSmallvilleand also the Xavier School of Gifted Youngsters inX2: X-Men UnitedandX-Men: The Last Stand.
Like Chloe Sullivan onSmallville, John Diggle was an original character created for the show that quickly became a fan favourite. Also like Ms Sullivan, he was quickly adapted into the comic universe in DC's New 52.
In the episode “Suicide Squad, ” a woman with a very distinct voice offers to help the group stop fighting because she is a therapist. This is none other than Harley Quinn who was a prison therapist when she met her future beau, The Joker. The character was originally played by Cassidy Alexa but Tara Strong was the one who provided voice-over work. Tara is known for voicing Harley Quinn in theBatman video gamesBatman: Arkham City, andBatman: Arkham Knight.
Arrowintroduced Barry Allen during season two a launch pad for his own superhero show, CW'sThe Flash.It was the start of a shared DC hero TV universe.
Just as withSmallville, virtually every single episode title is spoken aloud by a character in that respective episode.
Stephen Amell and Robbie Amell are everywhere on the CW.Stephen's (Oliver Queen/Arrow) cousin Robbie was the star ofThe Tomorrow People,and then joined CW'sThe Flash,as Firestorm.
The name “Green Arrow” came during the second season. Throughout the first season, he's casually referred to as "the green hooded guy" or "the vigilante" and things of that sort.
For decades, the Green Arrow character in the comics had bright blonde hair, wore a small mask to hide his identity, and had a famous, large, bold goatee.
On the show, Arrow wears only a green hood (large enough to put his face in shadow) and wears dark green face paint resembling a mask (until the end of season two). When DC relaunched Green Arrow with the New 52, he looks much more like his TV counterpart.
The character of John Diggle on the show is named after Andy Diggle, the comic writer responsible forGreen Arrow: Year One, a main source of inspiration for the show.
In season 3, a character named Ted Grant is introduced. In the comics, he's the hero known as Wildcat, who trained Black Canary, which is pretty much what he's doing in the show as well.