Kuwait’s Emir, Sheikh Sabah al-Ahmed al-Sabah, has died at the age of 91, state media report.
His 83-year-old half-brother, Crown Prince Sheikh Nawaf al-Ahmed, has been named by the cabinet as his successor.
In July, Sheikh Sabah was flown to the United States for medical treatment following surgery for an unspecified condition in Kuwait that month.
He had ruled the oil-rich Gulf Arab state since 2006 and had overseen its foreign policy for more than 50 years.
He was dubbed the “dean of Arab diplomacy” for his efforts to restore relations with states that backed Iraq during the 1990-1991 Gulf War, when Kuwait was invaded by Iraqi forces.
The emir also often acted as a mediator in regional disputes, including the ongoing diplomatic stand-off between Saudi Arabia, its allies and Qatar.
Kuwait similarly refrained from intervening in Syria’s civil war, instead hosting several donor conferences for humanitarian aid.
“Today we lost a big brother and a wise and loving leader… who spared no effort for Arab unity,” Jordan’s King Abdullah II wrote on Twitter in Arabic.
Abu Dhabi Crown Prince Sheikh Mohammed bin Zayed Al Nahyan, the de facto ruler of the United Arab Emirates, tweeted:
“Sheikh Sabah epitomised wisdom, tolerance, and peace and he was a great pioneer of Gulf cooperation.”
UN Secretary General António Guterres called the emir “an extraordinary symbol of wisdom and generosity, a messenger of peace, a bridge builder”.