Mehmed I, also known as Mehmed Çelebi or Kirişçi, was the sultan of the Ottoman Empire from 1413 to 1421. The fourth son of Sultan Bayezid I and Devlet Hatun, he fought with his brothers over control of the Ottoman realm in the Ottoman Interregnum (1402–1413). Starting from the province of Rûm he managed to bring first Anatolia and then the European territories (Rumelia) under his control, reuniting the Ottoman state by 1413, and ruling it until his death in 1421. Called "The Restorer," he reestablished central authority in Anatolia, and he expanded the Ottoman presence in Europe by the conquest of Wallachia in 1415. Venice destroyed his fleet off Gallipoli in 1416 as the Ottomans lost a naval war.

Bayezid I, also known as Bayezid the Thunderbolt, was the sultan of the Ottoman Empire from 1389 to 1402. He adopted the title of Sultan-i Rûm, Rûm being the Arabic name for the Eastern Roman Empire. In 1394, Bayezid unsuccessfully besieged Constantinople. Bayezid vanquished all the Beyliks and proceeded to conquer and vassalize the entirety of Anatolia. In 1402, he once more besieged Constantinople, appearing to find success, but he ultimately withdrew due to the invasion of the Mongol conqueror Timur. He defeated the Crusaders at the Battle of Nicopolis in what is now Bulgaria in 1396. He was later defeated and captured by Timur at the Battle of Ankara in 1402 and died in captivity in March 1403, which triggered the Ottoman Interregnum.