i have no idea, he's a poser far as I'm concerned, anything he's done some one else did, better, and to greater effect, and that's with out even leaving the FF games.
Killing player characters:
Exdeath, FF5: killed Gualf in a heroic last stand, where not even the most powerful of spells or attacks could harm him
Golbez, FF4: killed Tella indirectly, Tella used Meteo, which in Tella's old age he could not handle
FF2: LOTS of player characters die in this i'm told, never could get into the game but, there's a whole bonus section of the GBA release where you play as every one that died in the after life
Honorable mention, Lavos: he killed THE main character, Chrono, leaving you to finish the game with out one of the main party, unless you finished the side quest to bring him back, but that's be side the point.
also, note that all these characters are actually worth a damn in battle, and in most cases, also better over all characters
Killing Worlds:
Kefka, FF6: half way through, he destroys his world, and leaves it in such a state of ruin it's literally deing around him, not that he cares, its what he wanted.
Kuja, FF9: he dose it in a cut-scene, and its not the same world your on, but he dose, so it counts
Exdeath, FF5: technically, he actually remakes a world from two halves that where split, but it could also be argued, he destroyed those worlds to remake the old world as well.
Motivation:
Golbez, FF4: he's being controlled by a monster/demon/alien ... thing, called Zeromus, for his own resurrection/release but he was also jealous of Cecile (as stated in the DS remake)
Kefka, FF6: driven insane by the experiments done on him, i think .... i always chalked it up to him being FF's version of The Joker really ....
Exdeath, FF5: he wants the power of the void, for destroying everything? sorry, its been awhile since i played FF5, which is why Kuja isn't getting a spot here since i don't remember what his/her/it's deal was at all
compared to ....
Sepharoth.
player characters killed: one, and she wasn't really that good for anything anyway, even if you factor in Crisis Core it still only one player character
Worlds destoryed: LOL, moving on....
Motivation: but hurt about being 'a clone', except he's NOT a clone, he's genetically engineered, he has a mom, that carried him in her womb, a dad that knocked her up (FOR SCIENCE!!!) so his whole argument kinda falls apart. (not to mention FF7s whole idea of 'cloning' is fucked up anyway).
he dose how ever do one thing other FF villains haven't done well, stand around looking badass, cause... ya know, he's got nothing else going for him