Mustafa IV
Mustafa IV (September 8, 1779 – November 15, 1808) was the sultan of the Ottoman Empire from 1807 to 1808. His father was Abd-ul-Hamid I. During the reign of the reformist Selim III, Mustafa was looked upon favorably by the sultan.
However, when a janissary revolt rose up against Selim, Mustafa deceived the sultan and supported the janissaries who deposed the old Sultan, and made Mustafa the new ruler. Sympathy for Selim persisted, however, and in 1808 an army under Mustafa Bayrakdar set out for Istanbul in order to bring Selim back to the throne. In response, Mustafa ordered the execution of Selim as well as another brother, Mahmud. This would make Mustafa the only remaining male member of the royal line and, he hoped, thus defuse the rebellion by eliminating any other legitimate candidates for the throne. Selim was killed and his body was thrown before the rebels in mockery, but Mustafa was deposed anyway and replaced by Mahmud, who had escaped execution by hiding. Mustafa was put to death later in the year.
The Osmanli Dynasty ruled the Ottoman Empire from 1281 to 1923, beginning with Osman I (not counting his father, Ertuğrul), though the dynasty was not proclaimed until 1383 when Murad I declared himself sultan. Before that the tribe/dynasty might have been known as Söğüt but was renamed Osmanli in honour of Osman.
The sultan was the sole regent and government of the empire, at least officially. The sultan enjoyed many titles such as Sovereign of the House of Osman, Sultan of Sultans, Khan of Khans, Commander of the Faithful and Successor of the Prophet of the Lord of the Universe. Note that the first rulers never called themselves sultans, but rather beys. See the article on state organisation of the Ottoman Empire for further information on the sultan and the structure of power.
Hereditiary heads of the House of Osman since 1926:
When Mehmed II (the Conquerer) took over Constantinople on May 29, 1453, he committed a coup d'état by replacing the
Emperor of the Roman empire (a.k.a. the Eastern Roman Empire a.k.a. Byzantine Empire) with himself. He took the title Emperor (imparator)and protector of Orthodox Christianity.
He let himself be crowned Emperor by the Patriarch of Constantinople Gennadius Scholarius, whom he protected and whose stature he elevated into leader of all the Eastern Orthodox Christians.
So in addition to being Sultan of the Muslim citisens and Khan of the Turks, he was now also styled Emperor of the Romans.
As emperor of the Romans he laid claim to all the Roman territories and succesfully managed to put most of the Roman territories (except Rome and Italy) under his own control.
