The police in China have kept Mr. Liuâs wife, Liu Xia, under house arrest and smothering surveillance, preventing her from speaking out about Mr. Liuâs belated treatment for cancer.
âCanât operate, canât do radiotherapy, canât do chemotherapy,â Ms. Liu said in a brief video message to a friend when her husbandâs fatal condition was announced. The message quickly spread online.
Mr. Liuâs illness elicited a deluge of sympathy from officials, friends, Chinese rights activists and international groups, who saw him as a fearless advocate of peaceful democratic change.
âThe reaction to his illness shows how much he was respected,â said Cui Weiping, a former professor of literature in Beijing who knew Mr. Liu and now lives in Los Angeles. âPeople from all walks of life â friends, strangers, young people â have been outraged to hear that someone with terminal cancer was kept locked up till he died.â
Zeid Raâad al-Hussein, the United Nations high commissioner for human rights, said on Thursday, âThe human rights movement in China and across the world has lost a principled champion who devoted his life to defending and promoting human rights, peacefully and consistently, and who was jailed for standing up for his beliefs.â
Terry E. Branstad, the United States ambassador to Beijing, said in an emailed statement, âChina has lost a deeply principled role model who deserved our respect and adulation, not the prison sentences to which he was subjected.â
He added, âWe call on China to release all prisoners of conscience and to respect the fundamental freedoms of all.â
A year later, a court in Beijing tried and convicted Mr. Liu on a charge of inciting subversion. The petition and essays he wrote in which he upbraided and mocked the Chinese government were cited in the verdict. Mr. Liu responded to his trial with a warning about Chinaâs future.
âHatred can rot a personâs wisdom and conscience,â Mr. Liu said in a statement he prepared for the trial. âAn enemy mentality will poison the spirit of a nation and inflame brutal life and death struggles, destroy a societyâs tolerance and humanity, and hinder a countryâs advance toward freedom and democracy.â
By the time of the trial, Mr. Liu was already Chinaâs best-known dissident, and his fame grew even more when he was awarded the Nobel Peace Prize in 2010 while imprisoned in northeast China.
After his death was announced, Berit Reiss-Andersen, the chairwoman of the Norwegian Nobel Committee, said the âChinese government bears a heavy responsibility for his premature death.â
âLiu Xiaobo will remain a powerful symbol for all who fight for freedom, democracy and a better world,â Ms. Reiss-Andersen said by email. âHe was truly a prisoner of conscience, and he paid the highest possible price for his relentless struggle.â
Mr. Liu could not collect the Nobel Prize himself, and he was represented at the ceremony by an empty chair. His statement for his trial, which he was not allowed to read out, served in his absence as his Nobel lecture.
âXiaobo was wedded both psychically and physically to China and its fate,â Geremie R. BarmÃ©, an Australian Sinologist and a close friend of Mr. Liuâs, wrote in a tribute before Mr. Liuâs death. âIn the end, his words and deeds may have garnered him a Nobel Prize, yet in an authoritarian system, one that since 1989 has oscillated merely between the poles of the cruel and the pitiless, they sealed his fate.â
Confrontation and detention were nothing new to Mr. Liu.
He was born on Dec. 28, 1955, in Jilin Province, in northeast China. The son of a professor who remained loyal to the Communist Party, Mr. Liu made a vocation out of obdurate opposition to authoritarianism.
âHe was a dissident even among dissidents,â Yu Jie, a friend and biographer, said. Mr. Yu now lives in the United States.
He added, âLiu Xiaobo was willing to criticize himself and reflect on his actions in a way that even many activists in the democracy movement canât.â
Mr. Yu recalled the first time Mr. Liu spoke to him over the phone, in about 1999. âHe said, âIâve read your book, and thereâs a lot I disagree with,â â Mr. Yu said. âHe criticized me for about half an hour.â
Mr. Liu started out as a notoriously abrasive literary critic in Beijing in the 1980s. He was called a âdark horseâ who bridled at intellectual conformity, even in the name of reform. But he was increasingly drawn into political questions as Deng Xiaoping, the Communist leader, resisted matching economic liberalization with political transformation.
In 1989, he was a visiting scholar at Columbia University when students in Beijing occupied Tiananmen Square to demand democratic changes and an end to party corruption. He returned to Beijing to support the protests. He later described that time as a turning point, one that ended his academic career and set him irrevocably into a life of political opposition.
Mr. Liuâs sympathy for the students was not unreserved; he eventually urged them to leave Tiananmen Square and return to their campuses. As signs grew that the Communist Party leadership would use force to end the protests, Mr. Liu and three friends, including the singer Hou Dejian, held a hunger strike on the square to show solidarity with the students, even as they advised them to leave.
âIf we donât join the students in the square and face the same kind of danger, then we donât have any right to speak,â Mr. Hou quoted Mr. Liu as saying.
When the army moved in, hundreds of protesters died in the gunfire and the chaos on roads leading to Tiananmen Square. But without Mr. Liu and his friends, the bloodshed might have been worse. On the night of June 3, they stayed in the square with thousands of students as tanks, armored vehicles and soldiers closed in.
Mr. Liu and his friends negotiated with the troops to create a safe passage for the remaining protesters to leave the square, and he coaxed the students to flee without a final showdown.
âI understand what youâre feeling, but havenât you considered how as soon as the first shot rings out, Tiananmen Square will become a river of blood?â Mr. Liu told the students, as he recounted in a memoir published in 1989.
âIf he hadnât been on the scene, Iâm sure people would have died on the square. That was his pacifism in action,â said Liu Suli, a friend of Mr. Liuâs who stayed with him and his friends on Tiananmen Square on the night of June 3. âXiaobo had a kind of heroism complex that never left him.â
Mr. Liu was arrested days after the crackdown and spent 21 months in detention for supporting the protests. He lost his university lecturing job, his books were banned and the Communist Party labeled him a âblack handâ who had helped foment turmoil. His later support for American government policies, including the invasion of Iraq, also brought scorn.
But he was unbowed. In 1996, he was sent to a labor camp for three years after demanding clemency for those still in prison for joining the demonstrations.
Mr. Liu did not instigate Charter 08, but after he joined activists who were preparing to release it, he worked to make its demands acceptable to as many people as possible, tramping from door to door in Beijing to recruit prominent signers.
The petition at first drew 303 signers, including many prominent Chinese writers, academics, lawyers and former officials who were recruited by Mr. Liu. By May 2009, the number of signers had grown to over 8,600, including supporters living overseas.
âHe was able to span people inside and outside the system,â said Ms. Cui, the friend who also signed the charter. âHe also linked together opposition movements from different generations. I donât think anyone other than Liu Xiaobo could have done that.â
Mr. Liu and most other participants dismissed the risk that they could be severely punished. But his wife feared that the government would retaliate harshly. In the statement that Mr. Liu wrote for his trial, he thanked Ms. Liu for her âselfless love.â
âEven if I am crushed into powder, I will embrace you with ashes,â he wrote. âDearest, with your love, I will calmly face the impending trial, with no regrets for my choices, and will look forward with hope to tomorrow.â