The emir of oil-rich Kuwait, Sheikh Jaber al-Ahmad al-Sabah, has died, prompting 40 days of mourning.
Sheikh Jaber had led Kuwait for nearly 30 years
Sheikh Jaber, 78, had led the country since December 1977, but suffered ill health and was seldom seen in public after suffering a minor stroke in 2001.
Concerns have grown in recent years for the Gulf state's future leadership.
As expected, Crown Prince Sheikh Saad al-Abdullah al-Sabah, 76 and also said to be in poor health, has been appointed emir, the cabinet announced.
The announcement of the emir's death was made on state television. Government offices will close for three days.
Grieving Kuwaitis started to gather outside the late emir's Dasman Palace in Kuwait City on Sunday morning, the AFP news agency reports.
Sheikh Jaber, who held the post of prime minister from 1965-78 and was heir-apparent from 1966, was the 13th ruler of a 245-year-old dynasty.
He survived an assassination attempt in 1985 and the Iraqi invasion of Kuwait in August 1990.
He fled to Saudi Arabia, where he established a government in exile, returning in March 1991 after a massive US-led international military campaign ousted the Iraqi forces.
Under Sheikh Jaber's rule, Kuwait has built close ties with the US and the UK.
The first Arab country in the Gulf to have an elected parliament, its ruling family has recently come under increasing pressure to loosen its hold on power.
The BBC's Gulf correspondent, Julia Wheeler, says Sheikh Jaber was a decisive ruler in his early days who rose swiftly through the ranks.
However, his exile during the invasion by Iraq had a traumatic effect on him and he rarely appeared in public after his return, she says.
His later years will be remembered chiefly for electoral reforms which have seen women take public office and will give them the right to vote in parliamentary elections in 2007, our correspondent adds.
Crown Prince Sheikh Saad al-Abdullah al-Sabah is one of his distant cousins. He was chosen as the heir apparent in 1978.
The crown prince has been in ill health for several years
The crown prince was admitted to hospital in June last year suffering from a high level of blood glucose. He had previously been treated abroad for other ailments.
Although he was deputising for Sheikh Jaber, the crown prince's ill health meant many of the emir's daily duties were handed to Prime Minister Sheikh Sabah al-Ahmad al-Sabah.
Sheikh Jaber appointed Sheik Sabah - his own brother - as prime minister in 2003, breaking with a political tradition that crown princes also serve as heads of government.
Sheikh Jaber's death comes only 10 days after that of the ruler of Dubai, Sheikh Maktoum bin Rashid al-Maktoum, who died aged 62 while visiting Australia.