Description
This took a while due to his spiky almost Super Saiyan hair but I think I got it right by my usual standards. Forgive me if I got a few things off based on the pictures I used as a reference.
I've only ever played Final Fantasy VII but I researched the whole story for Final Fantasy VI and II as well. In the case of Final Fantasy II it's because I saw the Emperor on a "Top 20 Video Game Villains" list here (I'd link it if I knew how), seeing him on the list above Kefka with no Sephiroth intrigued me. He certainly feels compelling and that's BEFORE he dies, goes to hell, kills the devil, takes over hell, and returns to Earth in demon form stronger than ever, taking the capital city of hell with him. His second, final death is pretty spectacular. And while he does apparently have a name - Mateus - the fact that he's always referred to in-game as "The Emperor", and that he has no clear motivation other than being pure evil and power-hungry, makes him pretty mysterious. (Naturally I tried playing as him in Dissidia afterwards)
Hard to say who's the more impressive villain between him and Sephiroth. The Emperor returned from hell of his own accord stronger than ever, but Sephiroth was a lot harder to kill, taking an angelic form and then a spirit form each time his previous body was destroyed, and only when he died in spirit form did he go to his eternal resting place in Lifestream, but unlike the Emperor, he stayed there (unless you go by Advent Children as canon, in which case he was re-killed). Of course Sephiroth is still my favorite villain.
The Emperor belongs to Square.