As this shot is timed with the voice over of Idris Elba's voice, you have to imagine that this is him. Which begs the question: why cast someone as recognisable and as talented as him and make him a generic monster of the week? He doesn't look like a Jem Hadar exactly: he's conspicuously missing the bone spikes. So maybe this is the alien race whose head looks like ram horns from behind? His voice-over states that this is where the frontier pushes back," suggesting that the Enterprise's mission to seek out strange new worlds isn't actually welcome by the races who inhabit them. It becomes a question of where exploration becomes invasion.