At the age of 20, Prince Karim Al-Hussaini inherited the reins of a Shia Muslim lineage and used his entrepreneurship to become one of the world’s richest hereditary rulers.

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

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,