Suleiman I (Ottoman Turkish: سليمان اول, romanized: Süleyman-ı Evvel; Turkish: I. Süleyman; 6 November 1494 – 6 September 1566), commonly known as Suleiman the Magnificent in the West and Suleiman the Lawgiver (Ottoman Turkish: قانونى سلطان سليمان, romanized: Ḳānūnī Sulṭān Süleymān) in his realm, was the tenth and longest-reigning Sultan of the Ottoman Empire from 1520 until his death in 1566.^: 541–45 Under his administration, the Ottoman Empire ruled over at least 25 million people.

Suleiman succeeded his father, Selim I, as sultan on 30 September 1520 and began his reign with campaigns against the Christian powers in central Europe and the Mediterranean. Belgrade fell to him in 1521 and the island of Rhodes in 1522–23. At Mohács, in August 1526, Suleiman broke the military strength of Hungary.

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.^: 61

At the helm of an expanding empire, Suleiman personally instituted major judicial 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 Hürrem Sultan, a woman from his harem, an Orthodox Christian of Ruthenian origin who converted to Islam, and who became famous in the West by the name Roxelana, 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; Mehmed had died in 1543 from smallpox, and Mustafa had been strangled to death in 1553 at the sultan's order. His other son Bayezid was executed in 1561 on Suleiman's orders, along with Bayezid's four sons, after a rebellion. Although scholars typically regarded the period after his death to be one of crisis and adaptation rather than simple decline, the end of Suleiman's reign was 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.^: 11