The Kuwaiti royal palace has announced the death of Emir Sheikh Sabah al-Ahmad al-Sabah.
He was aged 91.
Al-Sabah was flown to the United States in July to receive medical treatment following a surgery.
He authorized his crown prince to temporarily take over some responsibilities until he recovered.
The 91-year-old emir ruled the small country and OPEC oil producer since 2006 and steered its foreign policy for more than 50 years.