They both have a wide network of soldiers and have bases far away from the other areas. Their minions also cause trouble throughout the whole game. Both have leaders that stay in the shadows until the end of the game.
Both are villains with dark themes and they are probably the oldest of their kind. Both are also complete Nightmare Fuel and way darker than what I would expect.
They both lead a group of instruments or devices and appear at the very end of their game. They are also involved in creating a mass production of their kind.