Whatever the true identity of the man in the mask, it's clear he is pretty important to Zoom. The villain gives Barry a quick beating when he discovers they've been communicating with him, and makes sure it can't happen again. Similarly, he's insistent that they won't be taking him, and he is the one who ends up left behind. There's also the fact that he's in a cell like Barry's, rather than Jesse's, suggesting he has superspeed or other powers. Of course, there's also that mask to consider. Sure, it could just be to protect his identity, but why go to all that effort? To hide it from Jesse, someone you plan on killing anyway? And why use something so elaborate? That means there's likely another purpose it - and him - is serving - could this be to do with Zoom's own speed, and perhaps how he takes it from other speedsters?