He's called The Inquisitor. He hunts Jedi. He's a Darth Vader sidekick.
The brand new Star Wars animated series Star Wars Rebels just released the very first, all new villain for the Empire. Take a gander at the Inquisitor.
The Inquisitor premiered at the New York Comic-Con panel thanks to this video hosted by Dave Filoni. The Inquisitor's job is to track down down the remaining Jedi Knights. He's under the control of Darth Vader—HOWEVER do not think that The Inquisitor negates Order 66. Everyone at the panel said this is still something very important to them and they want to continue to place importance around the fact that Luke is the last Jedi. And finally, even though we got this character there is still no announcement on which additional characters would be returning to the animated series.