The Night King

The Night King has risen an army of a dead. The army is composed of zombies that seek to kill anything in their path.

The Night King has a few leaders called White Walkers that can only be killed by Valyrian Steel and Dragonglass. The two items are rare, and this makes the Night King a seemingly unstoppable force.

The Night King is powerful, and since he's taken a dragon, he has the power of flight and fire. If he can't be stopped, the only thing against him taking the throne is the question of if there will be a throne left to take at the end of his march.