Paul Farmer, an American physician and medical anthropologist renowned for his innovative work in providing health care to poorer countries, died Monday at age 62, his Partners in Health group said.

The Boston-based organization said he "unexpectedly passed away today in his sleep while in Rwanda." It did not specify a cause.

Farmer's work on providing healthcare solutions through a vast network he helped set up in some of the world's poorest countries brought him wide acclaim. A 2003 book profiling him, "Mountains Beyond Mountains," called him "the man who would cure the world."

"Paul's passing is an immense loss to the world," former US president Bill Clinton, who worked closely with Farmer to help impoverished Haiti, said in a statement.

Clinton said he, his wife Hillary and daughter Chelsea -- who considered Farmer a mentor -- were "devastated" by the loss of "one of the most extraordinary people we have ever known."

"His pioneering work with Partners In Health touched millions of lives, advanced global health equity, and fundamentally changed the way health care is delivered in the most impoverished places on Earth," said the statement from the Clinton Foundation. "He was brilliant, passionate, kind and humble."

Samantha Power, a former US ambassador to the United Nations, tweeted that Farmer was "a giant" in his field.

"Devastating news," she posted. "Paul Farmer gave everything -- everything -- to others. He saw the worst, and yet did all he could to bring out the best in everyone he encountered."

And actor Edward Norton, a social and environmental activist, called Farmer "one of the most loving, funny, generous & inspiring people to grace humanity with his soul in our lifetimes."

Physician and medical anthropologist Paul Farmer is seen addressing a Haiti fundraising event in Los Angeles on January 7, 2017
Physician and medical anthropologist Paul Farmer is seen addressing a Haiti fundraising event in Los Angeles on January 7, 2017 GETTY IMAGES NORTH AMERICA via AFP / Michael Kovac

Working in Haiti in 1987, and living side-by-side with some of its poorest residents, Farmer co-founded Partners in Health to help devise and deliver better healthcare, first there and later in many other badly underserved countries.

A co-founder and close longtime associate was Jim Yong Kim, who went on to lead the World Bank from 2012 to 2019.

In 2009, Farmer succeeded Kim as chair of the Department of Global Health and Social Medicine at Harvard Medical School.

The same year he was named a UN deputy special envoy to Haiti, working with Clinton.

Farmer held that position at the time of the island's devastating 2010 earthquake, and soon was headed to Haiti on an airplane full of physicians.

A lifelong advocate for that poor Caribbean nation, Farmer co-founded the Institute for Justice and Democracy in Haiti.

Haitian Prime Minister Ariel Henry tweeted that he was "profoundly saddened" by the passing of a man he said was "a great friend of Haiti, whose works ... continue to benefit its people."

Farmer was editor in chief of the journal Health and Human Rights, and wrote extensively on the juncture of those two fields.

A recurrent theme was the deadly impact of poverty on health. Referring to the Ebola epidemic in Africa in 2014, Farmer, just back from Liberia, told the Washington Post: "This isn't a natural disaster. This is the terrorism of poverty."

Farmer, Kim and another Partners in Health co-founder, Ophelia Dahl -- daughter of British writer Roald Dahl and American actress Patricia Neal -- are featured in a 2017 documentary, "Bending the Arc."

In addition to Rwanda and Haiti, Partners in Health works in Kazakhstan, Lesotho, Liberia, Malawi, Mexico, Peru, Russia and Sierra Leone, as well as in Navajo communities in the United States.

Farmer was married to Didi Bertrand Farmer, a Haitian medical anthropologist.