The ruler of the United Arab Emirates' fourth-largest emirate died on Wednesday, the Gulf state's news agency said, and will be succeeded by his crown prince son Sheikh Saud.
Sheikh Saqr al Qasimi, believed to be in his late 90s, had ruled the northern emirate of Ras Al Khaimah for more than 60 years, dating back to before the UAE's inception in 1971. He had been in hospital for several months.
Ras Al Khaimah has been effectively under the leadership of Saud since his older half brother, Sheikh Khalid, was deposed as crown prince in 2003 by decree.
Khalid has campaigned for several years to regain the leadership, but most observers believe it is unlikely he will win power. His quest may complicate any transition in what is considered the least stable emirate of the seven-member UAE federation.
In 2003, tanks were dispatched to guard the palaces of the then newly appointed crown prince Saud, now in his 50s, a day after Khalid was dethroned.
The closest emirate to Iran, Ras Al Khaimah sits on the Strait of Hormuz, through which 40 percent of the world's seaborne oil passes.
The government announced an official mourning period with flags at half mast and said it would close government ministries and institutions.