His mild manners and gentle voice belie his conviction for his cause -- improving human rights in China.
"I feel that, in a dictatorship, if you want to be a person with dignity, if you want to be an honest person, you must fight for human rights and fight for freedom of speech," the writer and activist said in an interview in 2007. "Going to prison is part of that, and I have nothing to complain about."
As news spread Monday that Liu had been diagnosed with late-stage liver cancer in prison and granted medical parole, many of his friends and supporters said they feared the 61-year-old dissident was close to death and risked being made into a martyr
by the Communist authorities.
"Whether it was negligence or political murder, they have committed an unprecedented crime as no other government of the world has ever seen a Nobel Peace Prize laureate die in its custody," said Hu Jia, a leading Chinese human rights activist who has known Liu's wife for years and has served prison terms for his own advocacy.
Hu added that state security agents blocked him Tuesday from leaving home as he tried to drive to Shenyang in northeastern China, where Liu has been undergoing treatment at a local hospital since late May.
Liu has been allowed to see his wife and some relatives since being granted medical parole, a source close to his family told CNN.
The US government said it was gathering more information on Liu's medical and legal status.
"We call on the Chinese authorities to not only release Mr. Liu but also allow his wife Ms. Liu Xia out of house arrest, and provide them with the protection and freedoms -- such as freedom of movement and access to medical care of his choosing -- to which they are entitled under China's constitution and legal system and international commitments," a spokeswoman with the US embassy in Beijing said.
"This issue is China's internal affairs," said Lu Kang, a Chinese foreign ministry spokesman, on Tuesday. "No country has a right to interfere and make irresponsible remarks."
Liu was first jailed for his role in the 1989 pro-democracy movement after the bloody crackdown in Beijing's Tiananmen Square -- and later for petitioning for political reform and co-writing a paper on policy toward Taiwan that was at odds with the government stance.
His most recent conviction, on Christmas Day 2009, stemmed from his co-authorship of Charter 08, a manifesto calling for political reform and human rights in China. He received a surprisingly harsh 11-year prison term for "inciting subversion of state power."
In October 2010, while serving his sentence at Jinzhou Prison in northeastern China, Liu was named the winner of the Nobel Peace Prize
for "his long and non-violent struggle for fundamental human rights in China."
Liu's wife tweeted at the time that, upon hearing the news from her during a prison visit, he started to cry and said: "This is for the martyrs of Tiananmen Square."
Liu was born in December 1955 in Jilin Province. He moved to Beijing to pursue graduate studies and eventually became a university lecturer in the capital.
Even during his teaching days, however, the bespectacled intellectual was seen as a dark horse for his sharp rebuke to traditional ideologies and official doctrines.
Armed with a doctoral degree in Chinese literature, Liu was a rising-star literary critic in the 1980s. He spent time in the US and Europe as a visiting scholar, and turned his attention to the fight for democracy and human rights back home.
Having published numerous books -- on political and literary subjects -- overseas, Liu helped found the Chinese PEN Center, a literary and human rights organization, and served on its board of directors in the 2000s.
After the Norwegian Nobel Committee selected him as the recipient of 2010 peace prize, an infuriated Beijing tried to censor the news and boycott the award, insisting that Liu was a common criminal and the prize was nothing more than a Western plot against China.
The government also quickly put Liu Xia -- whom Liu Xiaobo married in 1996 while serving an earlier sentence -- under house arrest, rounded up his supporters and froze diplomatic relations with Norway.
Despite China's refusal to let Liu or a representative travel to accept the award, the Nobel ceremony organizers placed his citation and medal on an empty chair in a poignant event held in December 2010 in Oslo.
As Liu remained behind bars until recently, his wife -- an artist and a poet -- has paid a heavy price since his Nobel win.
With her communication with the outside world almost completely cut by the government, friends say she has been suffering severe depression and nervous breakdowns, especially after the authorities sentenced her brother to 11 years in prison over what supporters call trumped-up charges of business fraud.
"I feel Liu Xia is in more danger than her husband," said Hu, the activist. "She didn't choose this life -- but she's been forced to live in purgatory."
As for his own fate, nearly eight years before his Nobel award, Liu Xiaobo pointed to Russian physicist and Soviet dissident Andrei Sakharov -- who received a Nobel Peace Prize in 1975 -- as an example of the importance of individual responsibility in the fight for human rights.
"If China also has a dissident who becomes a Nobel Peace Prize laureate, it will be a big problem for the Chinese government," he told CNN in an interview in 2002. "They can't imprison a Nobel laureate forever."