Bayezid I
Beyazid I (ca 1354–1403; Bayezıt, nicknamed Yıldırım, the 'Thunderbolt') was the sultan of the Ottoman Empire from 1389 to 1402. He ascended to the throne following the assassination of his father Murad I and immediately had his younger brother Yakub strangled to prevent him from staging a coup.
In revenge for the assassination of Murad in the Battle of Kosovo, Beyazid massacred his Serb prisoners. Nevertheless, he was able to conclude a treaty with the Serb leader, Stephen Bulcovic, and granted Serbia considerable autonomy. In 1391 he laid siege to Constantinople. On the demand of the Byzantine emperor John V Palaeologus a new crusade was organized to defeat Beyazid. In 1396, the Christian allies, under the leadership of the Hungarian King and Holy Roman Emperor Sigismund, was defeated in the Battle of Nicopolis. The siege of Constantinople lasted until 1398 when the Byzantines paid a considerable tribute to break the siege.
In 1400, the Mongol warlord Timur Lenk had succeeded in rousing the local kingdoms that had been conquered by the Turks to join him in his attack on Beyazid. In the fateful Battle of Ankara, on July 20, 1402, Beyazid was captured by Timur and kept chained in a cage as a trophy. There are many stories about Beyazid's captivity, including one that describes how Timur used him as a footstool. One year later, Beyazid died — some accounts claim that he committed suicide.
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.
