DUBAI (Reuters) - Prominent Saudi Arabian rights activist Abdullah al-Hamid, imprisoned since 2013, died on Thursday, activists and a source close to him told Reuters.

Hamid, 69, died in the King Saud Medical City in Riyadh, having suffered a stroke on April 9 in prison, London-based Saudi rights group ALQST told Reuters. The news was confirmed by a close friend of Hamid’s who asked to remain anonymous owing to the sensitivity of the matter.

Hamid was one of the 11 founding members of the Saudi Civil and Political Rights Association (ACPRA), a group that documented human rights abuses and called for a constitutional monarchy. The group was disbanded in 2013 and all of its members eventually sentenced by Saudi courts on charges relating to its activities.

Hamid was arrested seven times, the last time in 2013, along with another founding member of ACPRA. He was sentenced in 2013 to 11 years in prison on charges including breaking allegiance to the ruler, questioning the integrity of officials, seeking to disrupt security and inciting disorder by calling for demonstrations, and instigating international organizations against the Kingdom.

The Saudi government media office did not immediately respond to a detailed written request for comment.

Hamid was often referred to by intellectuals and opposition figures as the father of the kingdom’s reformists.

“He was one of the first Saudi intellectuals that called for a constitution and democracy in the country, and he struggled with conservative clerics who declared him apostate,” ALQST’s Yahya Assiri said.

Sweden-based Right Livelihood Foundation condemned Saudi authorities “in the strongest terms for al-Hamid’s unlawful imprisonment and inhumane treatment that led to his death”.

The foundation in 2018 awarded him the Right Livelihood Award, also known as the alternative Nobel Prize, along with fellow activists Mohammad Fahad al-Qahtani and Waleed Abu al-Khair, for efforts to reform Saudi Arabia’s political system.

Hamid had a heart attack earlier this year while in al-Ha’ir prison, known for holding political dissidents and Islamic State militants. He was brought back to prison from hospital without having the surgery doctors said was necessary to treat his heart, the sources said, and his health continued to worsen.

He had a stroke on April 9 in prison and had been comatose in a Riyadh hospital since then.

The friend and Assiri told Reuters Hamid had not been allowed visits from family since his heart attack. Two of his brothers, Issa and Abdulrahman, also ACPRA members, remain in prison.

Hamid was buried in his home village of al-Qasayah in the central Qassim region -- one of the most conservative parts of the country -- on Friday, the first day of Ramadan.