(CNN) -- Fang Lizhi, a famed Chinese democracy activist, has died in the United States, where he fled in exile more than 20 years ago, fellow activists said.
He was 76.
Fang died Friday in Tucson, Arizona, according to Wang Dan, a prominent student leader of the 1989 Tiananmen Square student protests.
"My most, most respected teacher Fang Lizhi has died," Wang wrote on Facebook. "I am immensely sad. I hope that the Chinese people will forever remember him, that in our history there was a thinker named Fang (Lizhi) who inspired a 1989 generation and awakened the people to aspire to human rights and democracy."
He added, "Sooner or later, there will be a day when China will be proud of Fang Lizhi."
Fang, an accomplished astrophysicist, served as vice president of the elite University of Science and Technology at Hefei, Anhui province. He was dismissed from his job and expelled from the Communist Party in 1987, blamed for sympathizing with student protesters.
He was one of the three noted intellectuals who were publicly criticized during the "anti-bourgeois liberalization" campaign at that time, though Fang continued to speak out for democracy.
In early 1989, he wrote an open letter to Communist Party leader Deng Xiaoping, calling for the release of Chinese political prisoners.
After the bloody crackdown during the Tiananmen protests on June 4, 1989, Fang and his wife Li Shuxian sought refuge inside the U.S. embassy in Beijing.
A year later, they were allowed to leave China for Britain and were soon after granted political refuge in the United States.
Fang spent the past years doing research at the University of Arizona in Tucson.