He claims to be their friend, but he's really just trying to conquer the castle and kingdom for himself and then let everyone else fend for themselves.
He can brew ailments for his injured soldiers and knights to get them ready for battle again, but also to control his people. The evil wizard is a genius potion master. The Dragon Wizard is based on the minifig of the same name from the Dragon Mountain LEGO set. When he attacks, he throws a powerful fireball that does a significant amount of damage, and is also capable of ripping holes in structures and terrain. Periodically he will disappear under his hat, then reappear a moment later. The Dragon Wizard walks around with his arms out, then will stand still rubbing his hands in an evil gesture. His arms, hips and legs are also black, with additional printing on his legs resembling potion bottles and scissors.
His torso is black with red flame-looking printing on it, along with the printing of a silver chain with a dragon's head symbol on it. He has a long black beard over an angry-looking face. The Dragon Wizard wears a black pointed wizard's cap with a red dragon symbol printed on it.