Known best among us Westerners for his encounters and his gallantry with Richard Lionheart, Salah al-Din, was a Muslim conqueror who led a rags-to-riches story. From a minor lord is Mesopotamia, he rose to be the ruler of Egypt and one of the greatest leaders of the Muslim world. In a time when hatred and bigotry between the Christian and Muslim world ruled, his name was praised and revered by all. For this feat alone, he made this list.
Saladin fought everyone of the faction in the Middle-East: from Mesopotamia to Egypt to the Crusader to Syria and he even took on the famed Assassins! He was known as a generous man who gave a lot of his riches to his subjects.
In many ways Saladin is, to me, the epitome of what a D&D Paladin should be: honest, direct, constantly striving for the good of his people, willing to act swiftly when he thought his cause was right.
History has been kind to him and his legacy. I tried to think of Saladin as a bad guy, as someone who was legacy-hungry or obsessed with himself. But his actions throughout his life do not lend themselves to that.
Using him (as an opponent) Saladin is a man of principle above all. As an opponent, he is honorable and works within the law. He is the enemy who is one of ideology. He is not bad, but someone who supports a cause or a side different than the PCs'. It makes it that much more interesting because unlike the typical villain, simply raiding his castle and taking him out is likely to make things worse.
Using him (as an ally) A rather classic patron, this good guy seeks adventurers to further his agenda and do good in the world! Perhaps a bigger twist is that this patron's agenda actually is to do good! No dark purpose! I know! So novel!