Mehmed I: 5th Sultan of the Ottoman Empire

From 1413 to 1421, Mehmed I, also known as Mehmed Çelebi or Kirişçi, was the Ottoman Sultan. Sultan Bayezid I and Devlet Hatun had a fourth son. During the Ottoman Interregnum, he fought with his brothers for leadership of the Ottoman realm. Starting with the region of Rûm, he conquered Anatolia and later Europe, unifying the Ottoman kingdom by 1413 and controlling it until his death in 1421. With the conquest of Wallachia in 1415, he strengthened central control in Anatolia and increased the Ottoman presence in Europe. In 1416, Venice annihilated his fleet off the coast of Gallipoli, and the Ottomans lost a naval battle.

Mehmed was the fourth son of Sultan Bayezid I and one of his consorts, Devlet Hatun, born in 1386 or 1387. In 1399, he entered adolescence, as was the Ottoman norm. He was dispatched to gather experience as the provincial governor of Rûm Eyalet (central-northern Anatolia), which had just been liberated from the Eretnids. On 20 July 1402, his ancestor Bayezid was overpowered in the Combat of Ankara by Timur, the Turko-Mongol conqueror and king. From the fight, the brothers were saved. Bayezid Pasha rescued Mehmed and took him to his hometown of Amasya. Bayezid Pasha was later appointed as Mehmed's grand vizier (1413–1421). There was no controlled succession in the early Ottoman Empire. Every son, according to Turkish tradition, has the potential to succeed his father. Ertuğrul, one of Mehmed's brothers, died in 1400 when the next in line was still alive. Timur had Mustafa as a prisoner. Except for the minor siblings, the civil war left four princes, Mehmed, Süleyman, sa, and Musa, to fight for control of the remaining Ottoman domains. In recent history, these princes are commonly referred to as Çelebi.

However, Mehmed and Musa are given the title in modern texts. The title was rendered as Kyritzes in Byzantine sources, which was then adapted into Turkish as kirişçi. Mehmed Çelebi acted as Timur's subordinate during the early Interregnum. Along with the other princes, Mehmed issued coins with Timur's name "Demur han Gürgân" and his own "Mehmed bin Bayezid han" on them. This was most likely Mehmed's attempt to defend his conquest of Bursa following the Battle of Ulubad to Timur. Timur had already begun planning his return to Central Asia after Mehmed established himself in Rum. He didn't go any further in interfering with Anatolia's status quo.

Mehmed crowned himself Sultan in the Thracian city of Edirne, which was located in the European half of the empire, after winning the Interregnum. The area was separating the empire's Anatolian and European halves and Constantinople and its environs. It was still held by the Byzantine Empire when Mehmed I ascended to the throne. He solidified his position of power. He made Edirne the most significant of the dual capitals, and he defeated the Mamelukes in parts of Albania, the Jandarid emirate, and the Armenian Kingdom of Cilicia. Mehmed is usually regarded as the "second founder" of the Ottoman Sultanate, owing to his numerous accomplishments. Mehmed's brother Mustafa, who had been taken along with their father Bayezid I during the Battle of Ankara and held hostage in Samarkand, began his rule soon after. During the Interregnum, he resurfaced in Anatolia and urged Mehmed to partition the empire with him. Mehmed refused and went to combat with Mustafa's forces, handily beating them. Mustafa fled to Thessaloniki, a Byzantine city. The Byzantine emperor, Manuel II Palaiologos, deported Mustafa to the island of Lemnos after reaching an arrangement with Mehmed. Mehmed, on the other hand, had some issues. The first was Orhan, Mehmed's nephew, whom he saw as a challenge to his power, just like his late siblings had been. Manuel II Palaiologos allegedly intended to employ Orhan against Sultan Mehmed in a scheme involving him. The conspiracy was discovered by the Sultan, who had Orhan blinded for disloyalty.

Furthermore, the empire's populace had grown unstable and traumatized as a result of the Battle of Ankara and other civil wars. In the empire, a significant social and religious movement formed and became disruptive. Sheikh Bedreddin, a well-known Muslim Sufi and charismatic theologian led the movement. He was a prominent Ulema born in Simavna (Kyprinos), southwest of Edirne, to a Greek mother and a Muslim father. Musa, Mehmed's brother, had appointed Bedreddin as his supreme judge. In the Ottoman Sultanate, Bedreddin founded a populist religious organization with "subversive conclusions encouraging the suppression of socioeconomic disparities between rich and poor, as well as barriers between different types of monotheistic." Bedreddin's movement began in the European half of the empire and expanded into western Anatolia, successfully generating a popular social revolution and syncretism of the empire's different religions and sects. Sheikh Bedreddin began his revolt against the king in 1416. He was finally captured by Mehmed's grand vizier Bayezid Pasha and hanged in the city of Serres (modern-day Greece) in 1420 after a four-year struggle.

Mehmed I's tenure as Sultan of the re-united realm was barely eight years long before he died. But, during practically the entire 11-year Ottoman Interregnum between his father's detention at Ankara and his decisive victory over his brother Musa Çelebi at the Battle of Çamurlu, he had been the most powerful sibling fighting for the throne and de facto ruler of most of the empire. Mehmed blinded his nephew Orhan Çelebi before his death to ensure that the throne passed safely to Murad II. To assure the continued custody of his brother Mustafa, he chose to send his two sons Yusuf and Mahmud, to be kept as hostages by Emperor Manuel II. In Bursa, he was buried in a tomb erected by himself beside the famous mosque he built. The Green Mosque is so named because of its green glazed tile ornamentation. Mehmed I also finished a mosque in Bursa that his grandfather Murad I had started but abandoned during Bayezid's rule. In addition, Mehmed established two more notable institutions near his Green Mosque and mausoleum, one a school and the other a poor refectory. Both of which he lavished with royal riches.