BEIJING  - One of China’s most famous dissidents from the 1989 crackdown on pro-democracy activists has died in the United States, exiled dissidents said on Saturday. Fang Lizhi, 76, whom China had accused of counter-revolutionary crimes, lived in Tucson where he was a physics professor at the University of Arizona. He died of natural causes, according to the Twitter feed of Wu Renhua, a dissident living in exile in the United States. Exiled dissident Wang Dan, who topped a list of the 21 most-wanted student leaders from the time when the Chinese army crushed pro-democracy demonstrations centered on Beijing’s Tiananmen Square on June 4, 1989.