Sadruddin died Monday at Massachusetts General hospital in Boston, said Nasir Sunderji, an official of the Geneva-based Bellerive foundation, an environmental organization founded by Sadruddin.
There were no immediate details on the cause of death.
Sadruddin started his long career with the United Nations as an adviser to UNESCO for Afro-Asian projects. He was both the youngest and longest-serving U.N. High Commissioner for Refugees, taking over the post in 1965 at age 33 and staying for 12 years.
``All in UNHCR and the humanitarian community are deeply saddened by the passing away of Sadruddin Aga Khan,'' said Ruud Lubbers, the current refugee agency chief. ``He left an indelible print on UNHCR history, leading the agency through some of the most challenging moments.''
His name was ``synonymous with UNHCR,'' Lubbers said.
Sadruddin spearheaded U.N. efforts to cope with 10 million refugees from the breakup of Pakistan and creation of Bangladesh in 1971. He helped find homes for tens of thousands of Vietnamese who fled their communist homeland in the mid 1970s, and for Asians kicked out of Uganda by former dictator Idi Amin.
After resigning as refugee chief in 1977, Sadruddin held a series of senior U.N. roles, including coordinator for the U.N. humanitarian assistance programs for Afghanistan during 1988-1990 and special U.N. representative for humanitarian assistance for Iraq and Kuwait after the Gulf War in 1990 and 1991. He was once mentioned as a possible U.N. secretary-general.
One of his mottos was to keep a ``cool head and warm heart without getting cold feet.''
After he stood down from U.N. duties, he became increasingly involved in environmental protection of the Alps and rare Alpine birds. He was decorated with a long list of international awards, including the French Legion of Honor.
Sadruddin was born in Paris in January 1933 into a world of fabulous wealth as the son of Sultan Mohammed Shah, Aga Khan III - spiritual leader of the world's Ismaili Muslims.
He held French, Iranian and Swiss passports and was educated at Harvard University, allowing him to proclaim himself a ``citizen of the world.''
Yet despite the luxury associated with his famous family, he maintained that his lack of roots helped him to empathize with the plight of the displaced.
``If you cannot help the poor, you cannot save the rich,'' he once said.
Sadruddin was married for five years to a model, Nina Dyer, and their divorce in 1962 was headline news. But he quickly shed his playboy image and managed overall to avoid the gossip that dogged many members of the dynasty.
He shunned the racehorses, fast cars and diamonds favored by his half brother Aly, who was briefly married to the actress Rita Hayworth and who was the father of Karim - the Aga Khan IV.
Sadruddin once famously said that he disliked horse racing, and he listed his hobbies as sailing, skiing, hiking and flying kites.
Urbane and eloquent, he and his Greek-born second wife, Catherine Sursock, were familiar but discrete figures on the Geneva social scene. He was passionate about Islamic art and archaeology, as well as about bridging the understanding between different cultures.
``I was brought up in the Muslim religion,'' he told the London Daily Telegraph in a 1998 interview. ``My father insisted that I learn the Quran and encouraged me to understand the basic traditions and beliefs of Islam but without imposing any particular views. He was an overwhelming personality but open-minded and liberal.''
At his elegant Chateau de Bellerive on the shores of Lake Geneva, Sadruddin amassed a huge collection of priceless paintings, drawings and manuscripts from Turkey, Iran and India, dating from the 14th century.
``Fate uprooted my family from Iran over 130 years, ago,'' he said in the interview. ``I liked the idea of trying to getting some things back and taking care of them.''
Sadruddin is survived by his wife, Catherine, as well as his nephews, the Aga Khan and Prince Amyn Aga Khan; his niece, Princess Yasmin Aga Khan Embiricos; and his stepsons, Alexandre, Marc and Nicholas Sursock, the Bellerive foundation said.
Arrangements were under way to convey Sadruddin's body to Switzerland, it said. Details of funeral ceremonies were not yet announced.
Copyright 2002 Associated Press.