Singh, who held office from 2004 to 2014, was credited with having overseen an economic boom in Asia’s fourth-largest economy in his first term, although slowing growth in later years marred his second stint.

India “mourns the loss of one of its most distinguished leaders”, current Prime Minister Narendra Modi posted on social media platform X on Thursday, shortly after news broke of Singh’s passing.

“As our Prime Minister, he made extensive efforts to improve people’s lives.”

Singh was taken to a hospital in New Delhi after he lost consciousness at his home on Thursday, but could not be resuscitated and was later pronounced dead, according to a statement by the All India Institute of Medical Sciences.

“I have lost a mentor and guide,” opposition Congress leader Rahul Gandhi said in a statement, adding that Singh had “led India with immense wisdom and integrity”.

“Millions of us who admired him will remember him with the utmost pride,” said Gandhi, a scion of India’s powerful Nehru-Gandhi dynasty and the most prominent challenger to Modi.

Mallikarjun Kharge, leader of the opposition in parliament’s upper house, said “India has lost a visionary statesman, a leader of unimpeachable integrity, and an economist of unparalleled stature.”

President Droupadi Murmu wrote on X that Singh will “always be remembered for his service to the nation, his unblemished political life and his utmost humility”.

‘Mr Clean’

Born in 1932 in the mud-house village of Gah in what is now Pakistan, Singh studied economics to find a way to eradicate poverty in India and never held elected office before taking the vast nation’s top job.

He won scholarships to attend both Cambridge, where he obtained a first in economics, and Oxford, where he completed his PhD.

Singh worked in a string of senior civil posts, served as a central bank governor and also held various jobs with global agencies including the United Nations.

He was tapped in 1991 by then Congress prime minister P.V. Narasimha Rao to reel India back from the worst financial crisis in its modern history.

In his first term, Singh steered the economy through a period of nine-percent growth, lending India the international clout it had long sought.

He also sealed a landmark nuclear deal with the United States that he said would help India meet its growing energy needs.

U.S. Secretary of State Antony Blinken called Singh “one of the greatest champions of the U.S.-India strategic partnership”.

“His leadership in advancing the U.S.-India Civil Nuclear Cooperation Agreement signified a major investment in the potential of the U.S.-India relationship,” Blinken said in a statement.

Known as “Mr Clean”, Singh saw his image tarnished during his decade-long tenure when a series of corruption cases became public.

Several months before the 2014 elections, Singh said he would retire after the polls, with Sonia Gandhi’s son Rahul earmarked to take his place if Congress won.

But Congress crashed to its worst-ever result at that time as the Hindu-nationalist Bharatiya Janata Party, led by Modi, won in a landslide.

Singh—who said historians would be kinder to him than contemporary detractors—became a vocal critic of Modi’s economic policies, and more recently warned about the risks that rising communal tensions posed to India’s democracy.