A title bestowed upon the main commander of Zombie forces for that game. A player may only be Supreme Zombie Commander once, and afterwards must swear never to lead the zombies again.
They also do not appear every game. Rather, they appear as someone who takes control of the entire horde and leads it to victory against the humans in multiple battles. In games where zombies are unorganized, there is usually no Supreme Zombie Commander
Also seems to be a tendency for the best performing OZ to become a de-facto leader of the zombies, sometimes these de-facto leaders evolve into Supreme Zombie Commanders.