You know, to us Westerners, we could say "Sure, Gorbachov would be a good pick for Russia." But just because WE like him, doesn't mean the Russians do. The Russians consider Gorbachov a traitor. They freaking hate him. And you know what? Stalin was as horrible man, most of the western world agrees on this, and it's historical fact that he's to blame for tens of millions of deaths in Russia caused by starvation. But you know what? A lot of Russians love him. Love him a lot. Same with Mao, we hate him, sure there are some Chinese who hate him, but there are MANY people who love Mao. You have to pick leaders based on how their own people feel about them, not so much about how foreigners think of them. Our heroes could be their traitors.
Someone like Ayatollah Khomeni, well, that's iffy. Cyrus was the perfect pick for Persia, but they do need a 2nd leader. The problem is, do you pick someone beloved? Someone famous? Or someone with the biggest impact on their country? Xerxes? Darius? Certainly not the Shah, since he was a puppet, though.
and why mention Castro? The Americans hate Castro, and thats about it. To the Cuban people, Castro is so beloved you can't even imagine it. He rescued them from the American backed dictator Batista. Keep in mind that just because we love democracy and capitalism doesn't mean the rest of the world and other societies do. But anyways, Cuba is a country, a nation, but not so much a civilization, so not really appropriate to mention him.
And I think most of us agree Hitler would be a bad pick, since even his own people hate him. Plus, the Germans have enough leaders that unless you're playing a WWII mod/scenario, not worth adding. The game is Eurocentric enough as it is.