The administrative institutions characteristic of the late Ottoman Empire had already taken shape in the fourteenth century during the reigns of the first sultans. At the apex of the hierarchical Ottoman system was the person of the sultan, who acted in a number of capacities, political, military, judicial, social, and religious--under a variety of titles. Officially the sultan was called padishah. Among the Turks he was, as his nomadic warrior forebears had been, the khan, a master of the tribal ruling class. For his Christian subjects he was the "emperor"; later, among the Arabs under Ottoman rule, he was the imam, the protector of Islam. He was theoretically responsible only to God and God's law, the Islamic seriat , of which he was the chief executor. All offices were filled by his authority, and all legislation was issued by him in the form of a fireman. He was supreme military commander, and he had basic title to all land.