Liu Xiaobo, who on Friday was jailed for 11 years by a Beijing court for subversion, is a leading intellectual and social critic who has sought to bring political change and democracy to China. The 53-year-old writer, who was previously jailed for his involvement in the 1989 Tiananmen pro-democracy protests, was arrested a year ago after co-writing Charter 08, a widely circulated petition that called for political reform. The manifesto, which went online last year and has been signed by more than 10,000 people, calls for the protection of basic human rights and the reform of China's one-party communist system. It specifically demands the abolition of subversion in China's criminal code -- the very crime for which Liu has been jailed. 'We should make freedom of speech, freedom of the press and academic freedom universal, thereby guaranteeing that citizens can be informed and can exercise their right of political supervision,' the manifesto says. 'We should end the practice of viewing words as crimes.' Liu is also known for his efforts to help negotiate the safe exit from Tiananmen Square of thousands of student demonstrators on the night of June 3, 1989 when the military quelled six weeks of protests in the heart of Beijing. He was arrested immediately after the crackdown and released without charge in early 1991. Liu was re-arrested and served three years in a Chinese labour camp from 1996-1999 for seeking the release of those jailed in the Tiananmen protests and for opposing the government's verdict that they amounted to a counter- revolutionary rebellion. The holder of a doctorate in Chinese literature, Liu was once a professor at Beijing Normal University, but was banned from teaching at state institutions over his involvement in the 1989 protests. As a leading member of the Independent China Pen Centre, a grouping of Chinese writers, Liu had remained in close contact with key intellectuals and had been largely free to attend meetings and writer group activities despite constant police surveillance. Although Liu has been banned from publishing in China, many of his writings advocating greater democracy and respect for human rights have appeared in Hong Kong and overseas Chinese publications. Some of these writings, which can be downloaded from the Internet inside China, served as evidence in his trial, rights groups said. Liu -- who will turn 54 on Monday -- continues to command great respect from ordinary Chinese intellectuals, a fact that some say is also central to the Communist Party's decision to bring charges against him. Since his arrest, Western governments, rights groups, scholars, and a coalition of Nobel Prize winners have called for his release. The United States denounced his conviction on Friday. Liu has been honoured by Human Rights Watch, Reporters Without Borders and other rights groups. His essay 'The Noble Paradise of Power, the Hell for the Meek' won the Hong Kong Human Rights News Prize in 2004. Liu is married, but has no children. 