FFVI - Children of Vector

I havent watched the video yet (havent had the chance) but something I had always wondered about was Leo and Kefka's background in the game. How did such a kind and caring man come to be the General of such an evil intent army? And what was Kefka like BEFORE his maddening magic infusion experiment? Also, Celes. I understand she was kind of caring, considering she was imprisoned for treason after hearing about the poison (if my memory is correct... too many FF6 hacks lately. XD), but what about before that? I guess a lot about the Empire could be explained in this, possibly.