User blog comment:Nobody700/The reverse flash: Wally Edition/@comment-25640758-20160716202114

Maybe he's The Rival? If you don't know, he is basically the nemesis of Jay Garrick. Here's why I think that:

1. The lightning bolt on his chest seems similar to Jay Garrick's lightning bolt on his Flash costume.

2. The seasons usually have the main villain be related to a new character (assuming the black speedster is a major character). Season 1 introduced Barry, who's nemesis is the Reverse-Flash in the comics. In Season 2, Wally West appeared alongside Zoom. In Season 3, Jay Garrick was confirmed to return.