The Aga Khan, the spiritual leader of the world’s Ismaili Muslims, has died at the age of 88.

A post on social media from the Aga Khan Development Network says he passed away peacefully today in Lisbon, surrounded by his family.

The Aga Khan 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.