Prince Rahim al-Hussaini has been named the new Aga Khan, becoming the spiritual leader of around 15mn Ismaili Muslims worldwide following the death of his father in Lisbon aged 88.

The 53-year-old was appointed in his father's will, unsealed on February 5, as the fifth Aga Khan and 50th imam of the Nizari Ismaili branch of Shia Islam, continuing a 1,300-year dynasty that claims direct descent from the Prophet Muhammad. Ismailism shares its beginnings with other early Shi’ite Muslim sects that emerged during the succession crisis that spread throughout the early years of Islam. Prior to the collapse of the Pahlavi monarchy in Iran in 1979, the Ismailis held a royal title second only to the Shah of Iran Mohammad Reza Pahlavi. 

Through the Aga Khan Development Network (AKDN), Prince Rahim has focused on climate issues and will now oversee a vast portfolio of humanitarian institutions and business interests estimated to be worth between $1bn-$13bn, spanning airlines, real estate and media.

"My expectation would be that there is a continuation of that legacy, because it is ingrained in Islam and it is substantiated in these institutions," said Eboo Patel, founder of Interfaith America, who studied Ismaili institutions at Oxford University.

The late Aga Khan, who was given the title "His Highness" by Queen Elizabeth II in 1957, built the AKDN into a global force for development. it was particularly active in Asia and Africa through hospitals, schools and universities.

"We have no notion of the accumulation of wealth being evil," he told Vanity Fair in 2012. "The Islamic ethic is that if God has given you the capacity or good fortune to be a privileged individual in society, you have a moral responsibility to society."

Prince Rahim, educated at Phillips Academy and Brown University, inherits the leadership of a community known for pluralism and humanitarian work.

The AKDN has invested more than $1bn in Tajikistan alone since 1995, though recent tensions have seen Tajik authorities nationalise some properties amid separatism accusations.

In November, Central Asia specialist Bruce Pannier reported for bne IntelliNews on how the former imam of the Ismaili community served as the chief beneficiary to the Pamiri—but in a grievous blow to the minority, was being cut off from further cooperation by Tajikistan’s Rahmon regime.

"They have really been at the forefront of relief efforts and humanitarianism on behalf not only of Ismailis, but of all the people affected in the communities where they work," said Jonah Steinberg, associate professor at the University of South Carolina.

The succession marks a return to tradition after the late Aga Khan's own unexpected appointment.

In 1957, his grandfather bypassed other heirs to name the then 20-year-old Harvard student as successor, citing the need for youthful leadership in a rapidly changing world.

The late Aga Khan is survived by three sons and a daughter.