Slade Wilson, a.k.a. Deathstroke, is one of the more iconic DC villains to have appeared in CW's Arrow. The mercenary with the orange mask and deadly katana was the show's main villain early on, but hasn't been seen much since.
Arrow showrunner Marc Guggenheim may have recently revealed why. According to Comicbookmovie.com, a fan recently asked the showrunner about the "possible chance of either Slade or Walter returning throughout the rest of Season 4."
That led to Guggenheim replying with the following:
"The character of Slade Wilson is currently tied up in another DC project," Guggenheim said. "Walter is more likely."
What DC project might that be? The most obvious answer is something related to the DC Cinematic Universe, possibly even the upcoming Suicide Squad. The character is no stranger to the team of villains after all, and rumors have long been swirling that Scott Eastwood's Suicide Squad character in the film may be much more than the simple government soldier he appears to be.
If that is the case, it would be Deathstroke's cinematic debut, having appeared on the smallscreen multiple times in both Smallville and Arrow. The character of Slade Wilson, albeit a very different version of him, was also featured as the main villain of the Cartoon Network Teen Titans animated show. A Teen Titans live action show was rumored for a while, which very possibly could have involved Deathstroke, but no longer appears to be happening.
There is, of course, the question as to why the character's appearance on Arrow would have any effect on his movie appearances to begin with. DC is intent on keeping its television and film universes separate, so in theory two different versions of Deathstroke could co-exist. However, DC may want to limit the appearance of the character so that casual viewers don't get the two versions confused. We'll know the truth when Suicide Squad arrives in theaters on August 5, 2016.