Kuwait's emir, Sheikh Jaber al-Ahmad al-Sabah, has died at the age of 77, state television reported on Sunday.
The announcement was made in a statement from the royal court carried by the television in the tiny Gulf state, a key U.S. ally and OPEC member.
The emir, who suffered a brain hemorrhage in 2001, was the 13th ruler of a 245-year-old dynasty which has ruled Kuwait since the Anaiza tribe, to which the al-Sabahs belonged, migrated from the Arabian hinterland.
Since the fall of Saddam Hussein in neighboring Iraq in 2003 and U.S. calls for change in the Middle East, the ruling family had come under intense pressure from both Islamists and pro-Western liberals to loosen its grip on the government and share power.
Kuwait, a founder OPEC member, enjoys one of the world's highest standards of living, despite its reliance on oil exports, unpredictable oil income and huge losses from the 1990-1991 Iraq occupation.
The Gulf state sits on one tenth of the world's crude oil reserves, or 95 billion barrels.
Used as the main launchpad for the U.S.-led invasion of Iraq in 2003, Kuwait hosts up to 30,000 U.S. troops and some 13,000 U.S. citizens live in the country.
Kuwait, which a population of about 2.2 million, has cracked down on Islamists opposing the U.S. military presence there. Diplomats say radical Islam is taking hold among Kuwaiti youth.
In December, a Kuwaiti court sentenced to death six suspected militants linked to Osama bin Laden's al Qaeda for bloody attacks in the country.
The six were among 37 Islamists on trial as members of the "Peninsula Lions" group believed to be linked to al Qaeda in Iraq and Saudi Arabia.