Hussein bin Ali al-Hashimi (Arabic: , Al-usayn bin Al al-Hshim; 1 May 1854 4 June 1931) was an Arab leader from the Banu Hashim clan who was the Sharif and Emir of Mecca from 1908 and, after proclaiming the Great Arab Revolt against the Ottoman Empire, King of the Hejaz from 1916 to 1924. At the end of his reign he also briefly laid claim to the office of Sharifian Caliph. He was a 37th-generation direct descendant of Muhammad, as he belongs to the Hashemite family.

A member of the Dhawu Awn clan of the Qatadid emirs of Mecca, he was perceived to have rebellious inclinations and in 1893 was summoned to Istanbul, where he was kept on the Council of State. In 1908, in the aftermath of the Young Turk Revolution, he was appointed Emir of Mecca by the Ottoman sultan Abdul Hamid II. In 1916, with the promise of British support for Arab independence, he proclaimed the Arab Revolt against the Ottoman Empire, accusing the Committee of Union and Progress of violating tenets of Islam and limiting the power of the sultan-caliph. Shortly after the outbreak of the revolt, Hussein declared himself "King of the Arab Countries". However, his pan-Arab aspirations were not accepted by the Allies, who recognized him only as King of the Hejaz.

In the aftermath of World War I, Hussein refused to ratify the Treaty of Versailles, in protest at the Balfour Declaration and the establishment of British and French mandates in Syria, Iraq, and Palestine. He later refused to sign the Anglo-Hashemite Treaty and thus deprived himself of British support when his kingdom was attacked by Ibn Saud. In March 1924, when the Ottoman Caliphate was abolished, Hussein proclaimed himself "Caliph of all Muslims". In October 1924, facing defeat by Ibn Saud, he abdicated and was succeeded as king by his eldest son Ali. His sons Faisal and Abdullah were made rulers of Iraq and Transjordan respectively in 1921. After the Kingdom of Hejaz was invaded by the Al Saud-Wahhabi armies of the Ikhwan, on 23 December 1925 King Hussein bin Ali surrendered to the Saudis, bringing both the Kingdom of Hejaz and the Sharifate of Mecca to an end.

The Arab Revolt (Arabic: الثورة العربية, al-Thawra al-‘Arabiyya; Turkish: Arap İsyanı) or the Great Arab Revolt (الثورة العربية الكبرى, al-Thawra al-‘Arabiyya al-Kubrá) was a military uprising of Arab forces against the Ottoman Empire in the Middle Eastern theatre of World War I. On the basis of the McMahon–Hussein Correspondence, an agreement between the British government and Hussein bin Ali, Sharif of Mecca, the revolt was officially initiated at Mecca on June 10, 1916. The aim of the revolt was to create a single unified and independent Arab state stretching from Aleppo in Syria to Aden in Yemen, which the British had promised to recognize.

The Sharifian Army led by Hussein and the Hashemites, with military backing from the British Egyptian Expeditionary Force, successfully fought and expelled the Ottoman military presence from much of the Hejaz and Transjordan. The rebellion eventually took Damascus and set up the Arab Kingdom of Syria, a short-lived monarchy led by Faisal, a son of Hussein.

Following the Sykes–Picot Agreement, the Middle East was later partitioned by the British and French into mandate territories rather than a unified Arab state, and the British reneged on their promise to support a unified independent Arab state.