I find Alkiviades (Alkibiades) of Athens the most intriguing personality of the ancient world, and maybe of all times. Extremely capable, political genious, unlimited potential, great "behind the scenes" person, very able military commander, was also a serious case of degradation, decadence, hedonist, self-loathe, immoral bastard... an extremely complicated personality, but with a sole aim: his own well beeing. He pretty much shaped the history of the Greek world, by determining by his actions the outcome of the pelopponesian war.