The former leader of Egypt's Muslim Brotherhood, Mahdi Akef, has died in a Cairo hospital aged 89.

Akef, who headed the Brotherhood as the group's so-called "supreme guide" from 2004 to 2010, was diagnosed with cancer last year.

"My Father is in God's hands," his daughter, Alia, wrote on her Facebook page on Friday.

Akef was among hundreds of Brotherhood figures arrested in a heavy crackdown launched against the political organisation following the military's 2013 overthrow of President Mohamed Morsi, a member of the group and Egypt's first democratically elected president.

READ IS MORE: What is the Muslim Brotherhood?

He was initially convicted on violence-related charges and was sentenced to life imprisonment. The verdict was overturned on appeal, and he was facing a retrial.

His family had recently launched an online campaign to demand his release for health reasons.

'Reformist leader'

Akef was born on July 12, 1928, the same year the Muslim Brotherhood was founded.

He became aware of the organisation's teachings in his early teenage years and joined the Brotherhood in 1940.

A failed assassination attempt on Egyptian president Gamal Abdel Nasser in 1954 led to a wide-scale clampdown on the Brotherhood. Akef was imprisoned from 1954 until 1974.

For a large part of Hosni Mubarak's 40 years in power, which ended when he was overthrown as Egypt's president in the 2011 uprising, Akef was his main rival.

FROM THE ARCHIVES: Mahdi Akef speaks to Al Jazeera in 2005

In 2005, under Akef's leadership, the Brotherhood won 20 percent of the seats in Egypt's parliamentary elections.

"He has many achievements," said Khalil al-Anani, an academic and researcher of the Brotherhood.

"One of them was that he was one of the most reformist leaders of the Brotherhood since he took office in 2004. He initiated many changes within the movement and gave it a new flavour," he told Al Jazeera.

Writing on Twitter, the Palestinian group Hamas, which originated from the Muslim Brotherhood, described Akef's death as "the nation's loss and one of its most prominent figures".