Suleiman I (Ottoman Turkish: سلطان سليمان اول‎ Sultan Süleyman-ı Evvel; Turkish: Birinci Süleyman, Kanunî Sultan Süleyman or Muhteşem Süleyman; 6 November 1494 – 6 September 1566), commonly known as Suleiman the Magnificent in the West and Kanunî Sultan Süleyman (Ottoman Turkish: قانونى سلطان سليمان‎; "The Lawgiver Suleiman") in his realm, was the tenth and longest-reigning Sultan of the Ottoman Empire from 1520 until his death in 1566. Under his administration, the Ottoman state ruled over at least 25 million people.

Suleiman became a prominent monarch of 16th-century Europe, presiding over the apex of the Ottoman Empire's economic, military and political power. Suleiman personally led Ottoman armies in conquering the Christian strongholds of Belgrade and Rhodes as well as most of Hungary before his conquests were checked at the Siege of Vienna in 1529. He annexed much of the Middle East in his conflict with the Safavids and large areas of North Africa as far west as Algeria. Under his rule, the Ottoman fleet dominated the seas from the Mediterranean to the Red Sea and through the Persian Gulf.

At the helm of an expanding empire, Suleiman personally instituted major legislative changes relating to society, education, taxation and criminal law. His reforms, carried out in conjunction with the empire's chief judicial official Ebussuud Efendi, harmonized the relationship between the two forms of Ottoman law; sultanic (Kanun) and religious (Sharia). He was a distinguished poet and goldsmith; he also became a great patron of culture, overseeing the "Golden" age of the Ottoman Empire in its artistic, literary and architectural development.

Breaking with Ottoman tradition, Suleiman married Hurrem Sultan, a woman from his harem, a Christian of Ruthenian origin who converted to Islam, and who became famous in the West by the name Roxelana, purportedly due to her red hair. Their son Selim II succeeded Suleiman following his death in 1566 after 46 years of rule. Suleiman's other potential heirs, Mehmed and Mustafa, had died; the former had died from smallpox, and the latter had been strangled to death 13 years earlier at the sultan's order. His other son Bayezid was executed in 1561 on Suleiman's orders, along with his four sons, after a rebellion. Although scholars no longer believe that the empire declined after his death, the end of Suleiman's reign is still frequently characterized as a watershed in Ottoman history. In the decades after Suleiman, the empire began to experience significant political, institutional, and economic changes, a phenomenon often referred to as the Transformation of the Ottoman Empire.