Chinese dissident Bao Tong, a senior Communist Party official who was jailed after the 1989 Tiananmen Square protests and became a vocal critic of Beijing, has died at the age of 90, his son said on Twitter.

Bao had spent much of the past three decades under domestic surveillance or in prison after the Chinese military cracked down on student movements demanding democratic reform and an end to corruption.

“My late father…passed away peacefully on November 9, 2022 at 7:08 am,” his son Bao Pu wrote on Twitter Wednesday night.

A former member of the powerful Central Committee of the Chinese Communist Party, Bao Tong served as political secretary to reformist premier – and later party general secretary – Zhao Ziyang.

Zhao, once a rising star in the party leadership, clashed with hard-line peers over his sympathy for the student movement, eventually leading to his dismissal and house arrest.

Bao Tong, like Zhao a proponent of economic and political reform, was also arrested for supporting the movement and served seven years in prison before being released and placed under house arrest.

But his imprisonment did not prevent him from becoming a vehement critic of the Chinese government in articles and comments to the foreign press. He also fought in particular for Zhao Ziyang’s official rehabilitation until his death in 2005.

Convinced that China took the wrong path after the events in Tiananmen Square, he signed the Charter 08 manifesto, a widely shared online petition calling for political reform.

The manifesto, signed by more than 10,000 people, called for the protection of basic human rights and the reform of China’s one-party system.

Bao later became an outspoken critic of Chinese President Xi Jinping – the country’s most powerful leader since Mao Zedong – and spoke out against his efforts against corruption, which critics say was used to repress his opponents.

“Our system is based on corruption,” Bao said in 2013. “If I hit 10 tigers, 100 more come out. If I hit 100 flies, 1,000 come out.

“Why do they want political power? They want it to be corrupt.”