Murad II (1404–February 3, 1451) was the sultan of the Ottoman Empire from 1421 to 1451 (except for a period from 1444 to 1446). Murad's reign was marked by the long war he fought against the Christians of the Balkans and the Turkish emirates in Anatolia, a conflict lasting for 25 years. He was brought up in Amasya, and ascended the throne on the death of his father.

The Byzantines encouraged Mustafa Çelebi (known as Düzmece Mustafa) to try to create civil war and dethrone the young sultan. Mustafa defeated the Murad's army and declared himself Sultan of Adrianople (modern Edirne). The Ottoman army caught up with him in Ulubat, near Bursa, and executed him. Murad then formed a new army called Azeb in 1421, and marching through the Byzantine Empire, laid siege to their capital Constantinople. Whilst besieging that city, the Byzantines in league with some independent Turkish Anatolian states,sent the Sultan's younger brother Mustafa (who was only 13 years old) to rebel against the Sultan and besiege Bursa. Murad had to abandon the siege of Constantinople in order to deal with his rebellious brother. He caught Prince Mustafa and executed him. The Anatolian states that had been constantly plotting against him — Aydin , Germian , Mentese and Teke were annexed and henceforth became part of the Ottoman Empire.

He then went against Venice, the emirate of Karamanid, Serbia and Hungary. Karamanid was defeated in 1428 and Venice withdrew in 1432 following the defeat at the second Siege of Salonika in 1430. In the 1430s Murad captured huge territories in the Balkans and succeeded in annexing Serbia in 1439. In 1441 the Holy Roman Empire, Poland and Albania joined the Serbian-Hungarian coalition. Murad won the Battle of Varna in 1444 against János Hunyadi but lost the Battle of Jalowaz and was forced to abdicate.

In 1446 he regained command at the interference of the Janissaries and could crush the Christian coalition at the Second Battle of Kosovo (the first one took place in 1389). When the Balkan front was secured Murad turned east to defeat Timur Lenk's son, Shah Rokh , and the emirates of Karamanid and Çorum-Amasya. See the Wars of Murad II.