Rahim Al-Hussaini was named Wednesday as the new Aga Khan, spiritual leader of the world's millions of Ismaili Muslims. The 53-year-old succeeds his father, who died on Tuesday.

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,

Hussaini, son of Prince Karim Al-Hussaini Aga Khan IV, has been named in his father’s will as his successor to lead the Nizari Ismailis, a Shia Muslim denomination. We take a look at this branch of Shia Islam that has 15 million members worldwide.