The ailing leader of the United Arab Emirates, Sheikh Khalifa bin Zayed Al Nahyan, a key figure in his country’s history and one of the world’s richest kings, has died, the state-run Emirates News Agency reported on Friday. He is 73 years old.

No cause of death was given, but Sheikh Khalifa suffered a stroke in 2014 and has since stepped down from many of his public responsibilities. The government has announced that government offices and private businesses will be closed for three days starting Friday and 40 days of mourning will be observed across the Persian Gulf country.

Sheikh Khalifa became the head of state of the United Arab Emirates after the death of his father in 2004 and held various heavy titles as the country’s president; Prince of Abu Dhabi, the emirate of its capital city; And the head of its armed forces, the Investment Fund and the Petroleum Council.

But after his stroke, his public presence became increasingly rare, allowing his younger half-brother, Crown Prince Mohammed bin Zayed Al Nayan of Abu Dhabi, to act as the de facto head of state.

It is widely expected that Sheikh Mohammed will replace Sheikh Khalifa as head of the UAE, but there is no immediate word on the formal succession process.

The UAE is a federation of seven emirates led by Abu Dhabi which includes Dubai, a city famous for its futuristic architecture and reputation as a playground for the rich.

It is a close ally of the United States and its military has fought alongside the Americans in Afghanistan and elsewhere. Most of its resources come from oil and gas, although it has made better use of those resources than other rich countries in the Persian Gulf to diversify its economy through improvements in tourism, financial services and other sectors.