Now, even if you consider yourself a pretty prolific DC reader, you might be going "Who?" right now, and you're not alone. Antiphon isn't a very well-known villain, only popping up a couple of times in the second volume of Suicide Squad back in 2002. According to this report, though, he won't be alone in the film. He'll be leading the terrorist group Onslaught, which has been around in various forms since Suicide Squad #1 back in 1987 (they were called The Jihad back then). There's no word yet on who might be joining Antiphon on the Onslaught team, but the group will reportedly be hunting down superpowered people for their own reasons. As for Antiphon himself, he's described as a "burn victim" with a prosthetic leg, and Ed Harris is among the actors rumored to play him.
Of course, this is all unconfirmed at the moment, but if it's true it looks like Suicide Squad could be a special-ops-team-vs.-special-ops-team showdown.