The Ottomans were led by the Sultan in political matter and the Caliph in religious matters.
Ottomans
Mustafa Kemal Pasha.
No. The Ottomans adopted Islam and today some 99.5% of Turks are at least titularly Muslim.
A Caliph.
The military establishment is one of the attributes that made the Ottomans expand their empire with much success.
The Sultan.
Yes it was .
1453
The ottomans were Muslim.
I am not sure what "the" Islamic Empire is. There have twenty-five or so different Islamic Empires. However, there are some territories that the Ottomans failed to conquer that were part of other Muslim States either concurrently or in times past. Persia, India, Spain, and Indonesia all come to mind.
The Ottomans
Mohammed, the final Islamic prophet was Islam's first leader.