Easy answer, for me.
Iskandar! The King of Conquerors!
He's Alexander the Great, son! He's a heroic spirit, which means he was so awesome that the Holy Grail was like "you are totally awesome, let me save a copy of you so that you can fight a bunch of other awesome historical dudes in my wars, and shit." And he goes along with it, but only because he wants to conquer the world.
"Doesn't wanting to conquer the world make him a bad guy?" you ask, because you don't know things. No, it doesn't. Because Broskander lives by a code: "To win, but not destroy; to conquer, but not humiliate: That is what true conquest is!" So basically, he wants to beat you - but instead of killing or humiliating you, he wants to make you see how absolutely baller he is, and join his crew. He's even willing to sit down and drink with his enemies if he thinks that there's a chance they can be bros.
His entire super-power, the Ionion Hetairoi, is based on the fact that his followers were so loyal to him that they want to serve him for all eternity. He is literally a world conqueror powered by friendship. Broskander is the best waifu, with the pimpest cape.