Sheikh Khalifa bin Zayed Al Nahyan, the ruler and president of the United Arab Emirates who had been suffering from a long illness, passed away on Friday at the age of 73.

Sheikh Khalifa oversaw much and contributed to the country's economic growth, and his name was immortalized in the world's tallest building, Burj Khalifa, after rescuing Dubai which was paralyzed by debt during its financial crisis more than a decade ago.

However, after suffering a stroke and undergoing emergency surgery in 2014, a decade into his presidency, he ceased to participate in the daily affairs of governing the country.

The recent years of his life witnessed the rise of his half-brother Abu Dhabi Crown Prince Mohammed bin Zayed to become the de facto ruler and decision-maker in major foreign policy decisions, such as joining the Saudi-led war in Yemen.

The Crown Prince, who is also the Deputy Supreme Commander of the Armed Forces, fostered the emerging UAE relations with Israel after normalization in 2020.

The United Arab Emirates announced a 40-day mourning period and a suspension of work in the government and private sector for three days, including flying flags at half-mast.

No immediate announcement was made about Khalifa, although Sheikh Mohammed bin Zayed is expected to assume the presidency at a time when oil prices are rising.

Sheikh Mohammed bin Zayed wrote on Twitter after the official announcement of his brother's death through government media, "The UAE has lost a loyal son and leader of its blessed empowerment march." "Khalifa bin Zayed, my brother, my supporter, and my teacher, may God Almighty grant you eternal peace."

In a statement, US Secretary of State Antony Blinken described Sheikh Khalifa as a "true friend of the United States," adding that the US remains committed to a deep friendship and cooperation with the UAE.

Vice President Kamala Harris also expressed her condolences to the ruling family, as condolences poured in from across the region and the world, led by Arab state leaders.

Sheikh Khalifa is the eldest son of Sheikh Zayed bin Sultan Al Nahyan, who is highly respected by Emiratis as the founding father of the country.

Although he had been out of sight since suffering a stroke, the image of Sheikh Khalifa was widespread everywhere, overseeing every hotel lobby and major government offices throughout the country.

Emirati government media occasionally published rare photos and videos of Sheikh Khalifa.

The president holds the strongest position among the seven semi-autonomous emirates in the UAE, which stretch along the shores of the Arabian Gulf and Gulf of Oman.

Historically, the president is from Abu Dhabi, the largest and richest of the seven emirates.

Sheikh Khalifa increasingly used Abu Dhabi's oil wealth to attract cultural and academic centers, such as the Louvre Museum branch, the campus of New York University, and Sorbonne.

He also oversaw efforts to move the OPEC country beyond its reliance on petrodollars with investments in renewable energy research.

Last year, the UAE announced a pledge to reach net zero emissions by 2050, even as it expanded investments in oil and gas for export.

He is credited with overseeing the establishment and growth of the Abu Dhabi Investment Authority, now one of the largest sovereign wealth funds in the world with assets nearing $700 billion, according to Sovereign Wealth Fund Institute estimates.

Sheikh Khalifa was born in 1948 in the inner Al Ain oasis near the border with Oman. He trained at Sandhurst, the Royal Military Academy in England. In 1969, Sheikh Khalifa was appointed Prime Minister of Abu Dhabi and Minister of Defense in the emirate, which later became the core of the UAE Armed Forces.

Khalifa helped enhance the regional image of the UAE by expanding its army with massive purchases from American arms manufacturers.

He deployed fighter jets for the NATO-led mission against Muammar Gaddafi's regime in Libya in 2011.

In 2014, the UAE became one of the leading Arab participants in US-led airstrikes against ISIS in Syria.

US Defense Secretary Lloyd Austin said the United States will honor Sheikh Khalifa's legacy "through our strong defense partnership with the United Arab Emirates."

The commander of the US Central Command in the Middle East, General Michael Kurilla, said the "strategic partnership between our militaries is solid."