Who is Fulcrum?

Most likely we will discover the mysterious Fulcrum's identity in the upcoming season finale, but anyone have any theories on who he/she may be?



My two top hopes are Ahsoka- just makes sense, and would set up for more Vader (and perhaps even an appearance by Emperor ;)) and Darth Maul. I'm pretty positive it's not Maul, but think about how helpless the team would be if they were wedged between arguable the two best villains in Star Wars to date!