Muslims do not have one leader, like a pope. There are many many scholars who are well-respected by most Muslims, though.
Allah is the spiritual leader of muslims.
A kafir can not lead Muslims. Only a Muslim can lead Muslims.
Saladin led the Muslims in some of the Crusades.
I'm not Muslim but I think their leader is Mohammed.
Jesus
Ali
saladin
Agakhan is leader of Ismaili muslims.
Iman is not a religios leader. Iman is what Muslims call their faith.
An Imam
Imam, sheikh, Ayatuallah, ....