PARIS >> The Aga Khan, who became the spiritual leader of the world’s millions of Ismaili Muslims at age 20 as a Harvard undergraduate and poured a material empire built on billions of dollars in tithes into building homes, hospitals and schools in developing countries, died Tuesday. He was 88.

His Aga Khan Development Network and the Ismaili religious community announced that His Highness Prince Karim Al-Hussaini, the Aga Khan IV and 49th hereditary imam of the Shiite Ismaili Muslims, died in Portugal surrounded by his family.

On Wednesday, his son Rahim was named the Aga Khan V, the 50th hereditary imam of the Shiite Ismaili Muslims, in accordance with his father’s will.

The Ismaili community’s website said the late Aga Khan’s burial will be held in the coming days, followed by an homage ceremony.

Considered by his followers to be a direct descendant of the Prophet Muhammad and treated as a head of state, he was a student when his grandfather named him as successor to lead the diaspora of Ismaili Muslims, passing over his playboy father and saying his followers should be led by a young man “who has been brought up in the midst of the new age.”

Over decades, the Aga Khan evolved into a business magnate and a philanthropist, moving between the spiritual and the worldly with ease.

Ceremonies were held in Ismaili communities in the U.S. and elsewhere in the world on Tuesday and Wednesday.

U.N. Secretary-General António Guterres called him “a symbol of peace, tolerance and compassion in our troubled world.” Canadian Prime Minister Justin Trudeau called him a very good friend and “an extraordinarily compassionate global leader.”

Condolences poured in online from charity groups he supported, as well as the equestrian world, where he was a well-known figure.

The Aga Khan was given the title of “His Highness” by Queen Elizabeth in July 1957, two weeks after his grandfather the Aga Khan III unexpectedly made him heir to the family’s 1,300-year dynasty as leader of the Ismaili Muslim sect.

He became the Aga Khan IV on July 11, 1957, in Geneva, Switzerland and later that year had an installation ceremony in Dar es Salaam, Tanzania, on the spot where his grandfather once had his weight equaled in diamonds in gifts from his followers.

He had left Harvard to be at his ailing grandfather’s side, and returned to school 18 months later with an entourage and a deep sense of responsibility.

“I was an undergraduate who knew what his work for the rest of his life was going to be,” he said in a 2012 interview with Vanity Fair magazine. “I don’t think anyone in my situation would have been prepared.”

A defender of Islamic culture and values, he was widely regarded as a builder of bridges between Muslim societies and the West despite — or perhaps because of — his reticence to become involved in politics.

The Aga Khan Development Network, his main philanthropic organization, deals mainly with issues of health care, housing, education and rural economic development. It says it works in over 30 countries and has an annual budget of about $1 billion for nonprofit development activities.

He is survived by three sons, a daughter and several grandchildren.