The Emperor Gestahl is one of the antagonists of Final Fantasy VI. His name translates to something like "steel" in German, although it could also be a reference to the Heideggerian concept of "Gestihl", the "framing" of technology and maybe I should have saved that for something past the second sentence.
In the game, Gestahl is the emperor of the expansionistic Southern Continent, which is engaging in a conquest of the towns of the northern continent. Which is in many ways, if you know your JRPGs, some pretty standard stuff. Gestahl is also taking "espers" (supernatural entities) and turning them into "magicitie", a mixture of magic and technology. He has several top generals, including General Leo Christophe, Celes Chere (who switches sides) and Kefka, who becomes the game's chief antagonist.
Halfway through the game, Gestahl makes a treaty with other nations, and at a lavish banquet apologizes for what he has done and makes peace with the player characters. Seemingly. It is all a ruse: he betrays the player characters and General Leo, and then, on a floating continent in the middle of the game, is unceremoniously betrayed by Kefka, being stomped and thrown into the air. After his death, he is not mentioned for the rest of the game, with the focus turning to Kefka, an insane clown.
For most fans, the over-the-top, maniacal Kefka gets most of the attention, with the stodgy Emperor Gestahl seeming like merely a supporting character. However, he is the launch point for the entire plot, since he is the one that enables Kefka in the first place. He also, in a key way, shows a more evil nature than Kefka: he appears rational, appears ready to deal with the characters, and makes false statements of remorse about his past action.
To describe it philosophically, Gestahl represents evil as motivated by reductive, extractive rationalism. Kefka represents evil as motivated by total nihilism. And in reality, as in the game, the first always leads to the second, and there is no way to "deal safely" with people like Emperor Gestahl, no matter their mastery of the appearance of politeness and civility.