Emperor Mateus

The Emperor of Palamecia is the final boss of Final Fantasy II. He is responsible for the demonic armies that have been plaguing the Kingdom of Fynn. Firion and his allies must face him twice. First, they must defeat him in the whirlwind he summons. Before they can get to him though, he calls his guards to attack the heroes. The heroes must fight their way past two waves of guards to reach the Emperor. When they finally get to him, he is joined by two more of his guards and a golem. After he is killed for the first time, Leon tries to assume the throne, but when the heroes arrive at Palamecia to confront Leon, the Emperor returns from the dead in a demonic form and transforms Palamecia Castle into Pandemonium. The heroes are forced to travel through the Jade Passage to reach Pandemonium and defeat the Emperor once and for all.

Light Emperor (Dawn of Souls)
In the Soul of Rebirth bonus quest in Final Fantasy I & II: Dawn of Souls, there is an angelic version of the Emperor serving as that bonus quest's final boss. He resides in a castle that resembles Pandemonium (it is simply Pandemonium's mirror image: left is right and right is left) and when confronted by the four slain heroes, asks for forgiveness. However, the slain heroes see a vision of the battle against the "Dark Emperor" and realize that the "Light Emperor" is tricking them. They defeat him in battle and are allowed to rest in peace.