Tonight is a big night or Digger Harkness, also known as the DC Comics villain Captain Boomerang. Besides being the target of The Arrow's investigation on The Flash, Boomerang has been cast in David Ayer's upcoming feature film adaptation of Suicide Squad.
Like Green Arrow, Boomerang typically competes with the metahuman community by creating trick boomerangs that go beyond the limits of normal weapons. He is usually, but not always, depicted as speaking with an Australian accent.
While often a member of The Flash's Rogues Gallery, Captain Boomerang is one of the Rogues most likely to be found facing off against other DC heroes; in Identity Crisis, it was revealed that the classic Boomerang had a son, and that's the character who ultimately took over the role when the elder Captain died in the act of murdering Robin's father.
In the comics, Harkness has also been associated with the Suicide Squad, in both the comics and on Arrow, which makes it perhaps unsurprising that he's on the Squad in the movies.
As Owen Mercer, Harkness' son and the second Captain Boomerang, the character was able to utilize super speed like The Flash, via the Speed Force.
The character also appeared in Batman: Assault on Arkham, played by Greg Ellis. In Suicide Squad, he will be played by Jai Courteney, and on tomorrow night's Arrow, Nick Tarabay will reprise the role from last week's episode.