A plug or two for Greyhawk
Name: Iuz
1) Track record: A demi-god who conquered his own country out of wildlands, was magically imprisoned with other minor gods, and was released by adventurers. In From the Ashes and later versions of Greyhawk, he's launched a major war and conquered several other countries, including a country full of knights (the Shield Lands), a country full of bandits and thieves (the Bandit Kingdoms), and lots of tough barbarians (of vaguely American Indian types in the Rovers of the Barrens, and vaguely Slavic in the Stonehold), through trickery and humanoids and demons, oh my!
2) Success rate: He's got a big empire, and there's no adventure where he's on screen to be killed, so far as I recall.
3) How close to winning they get: He's not even losing yet.
4) Style: Over the top, like a cross between a Roman emperor and a bad hair/death metal band. He's got a road made of skulls, lit by torches made from burning his enemies alive. Also, nobody says his name -- he's just The Old One.
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Name: Iggwilv, the Witch-Queen
1) Track record: Iuz's mom, mother of a hot vampire daughter who's entombed in one of the cooler dungeons in Greyhawk. Wrote THE book about demonology.
2) Success rate: Well, her empire only lasted about 10 years, but she was still a cover girl in Dungeon, and she got mentioned in Dragon, many, many times.
3) How close to winning they get: Define winning. She doesn't have any petty human-type goals, so far as I can see. She doesn't seem to be dead yet, but she's not doing anything much right now, so she must be set for a Big Comeback!
4) Style: A not, dark-haired female spellcaster who wears black all the time (including a cape made from the skin of a demon, a gift from a demon lover). She captured a demon-lord to imprisons him and steal his power -- and have a demi-god kid with him. She's like a bad-ass Elvira!