Orhan Ghazi (اورخان غازی; Orhan Gazi, also spelled Orkhan, 1281 – March 1362) was the second bey of the Ottoman Beylik from 1323/4 to 1362. He was born in Söğüt, as the son of Osman I.
In the early stages of his reign, Orhan focused his energies on conquering most of northwestern Anatolia. The majority of these areas were under Byzantine rule and he won his first battle at Pelekanon against the Byzantine Emperor Andronikos III Palaiologos. Orhan also occupied the lands of the Karasids of Balıkesir and the Ahis of Ankara.
A series of civil wars surrounding the ascension of the nine-year-old Byzantine emperor John V Palaiologos greatly benefited Orhan. In the Byzantine civil war of 1341–1347, the regent John VI Kantakouzenos married his daughter Theodora to Orhan and employed Ottoman warriors against the rival forces of the empress dowager, allowing them to loot Thrace. In the Byzantine civil war of 1352–1357, Kantakouzenos used Ottoman forces against John V, granting them the use of a European fortress at Çimpe around 1352. A major earthquake devastated Gallipoli (modern Gelibolu) two years later, after which Orhan's son, Süleyman Pasha, occupied the town, giving the Ottomans a strong bridgehead into mainland Europe.
According to Muslim scholar Ibn Battuta, Orhan was "the greatest of the Turcoman kings and the richest in wealth, lands, and military forces".
Osman Gazi died in either 1323 or 1324, and Orhan succeeded him. According to Ottoman tradition, when Orhan succeeded his father, he proposed to his brother, Alaeddin, that they should share the emerging empire. The latter refused on the grounds that their father had designated Orhan as sole successor, and that the empire should not be divided. He only accepted as his share the revenues of a single village near Bursa.
Orhan then told him, "Since, my brother, thou will not take the flocks and the herds that I offer thee, be thou the shepherd of my people; be my Vizier." The word vizier, vezir in the Ottoman language, from Arabic wazīr, meant the bearer of a burden.