After the communist regime seized control of China in 1949, the government's various political campaigns purged tens of millions of people through executions, prison terms and so-called re-education efforts. The greatest achievement of Hu Yaobang - the country's liberal leader whose death sparked the massive Tiananmen protests of 1989 - was to clear millions of political victims of false charges, and to free the country from the strictures of Maoist dogma, say Hu's former staff members and party colleagues.
"Hu Yaobang launched the campaign to vindicate people who were wrongly accused. Without him, I doubt whether it could have taken place at all," said He Fang, 91, a former senior official at the foreign ministry.
Once the party's top leader as general secretary, Hu prodded officials to make governing more transparent and to loosen economic controls. His forced resignation in 1987 and death two years later sparked an immediate outcry from students hungry for democracy and furious with the party's corruption.
Twenty five years later, his former staff and colleagues have a renewed appreciation for Hu's work.
In the Anti-Rightist Movement that began in 1957, hundreds of thousands of intellectuals - many of them critical of Mao Zedong - were sent to re-education camps where hard labour would supposedly reform their minds. Next, during the Cultural Revolution from 1966 to 1976, millions of Chinese were beaten, tortured and executed by the government.
People with backgrounds from the "five black categories" - landlords, rich farmers, anti-revolutionists, bad elements and capitalists - were arbitrarily persecuted during the tumultuous movement.
During the Cultural Revolution, officials beat He, the former foreign ministry official, and sent him to nine years of hard labour as an "anti-revolutionary revisionist".
In 1959, officials denounced him as a "right-leaning opportunist" of an anti-party clique because he was an assistant to Mao's rival, deputy foreign minister Zhang Wentian.
After Hu launched his 1979 effort to clear victims, He was rehabilitated. Before that, it would have been impossible for someone whose name had not been cleared to hold a job or receive social welfare benefits. He rebuilt his career, later leading the Japan Institute at the Chinese Academy of Social Sciences.
During Mao's life, anyone who expressed doubts about his supreme authority could be jailed or executed. Two years after the chairman's death in 1976, which snuffed out the Cultural Revolution, Hu helped launch a national ideology debate. When Hu was deputy leader of the party's central school, he permitted and edited a commentary in a party publication that declared, "practice is the sole criterion for testing truth". The article challenged citizens to not accept dogma and to assess for themselves the doctrine that Mao's words represented absolute truth. It ushered in a reassessment of the leader's legacy.
Du Daozheng, the former director of Xinhua's domestic department, was active at the news agency in the late 1970s and regularly spoke with Hu, then the party's propaganda chief. Du said Hu faced great political risk by embarking on a campaign that offended powerful party conservatives.
"Hu Yaobang was at the forefront of this debate over the criterion of truth," said Du, 91, now publisher of the outspoken political magazine Yanhuang Chunqiu. "On the [political] struggle over this issue, he was absolutely in the leadership position."
Early in his career with the communists, Hu was known for prodding leaders to think critically about Mao's acts.
Zhong Peizhang, who was deputy chief editor of the China Youth Daily in the 1950s and 1960s, worked with Hu for more than a decade when Hu chaired the Communist Youth League. He recalled how Hu's push for liberation "awakened" him from Mao's oppressive doctrine.
"My mind became gradually liberated," said Zhong, 90, who was sent to the countryside as a rightist in the 1950s as part of Mao's "thought reform" effort to intimidate intellectuals into silence. "Before, we believed Mao was always right and he represented the truth."
Dai Huang, a veteran Xinhua journalist, was branded a rightist in 1958 for doubting the supreme authority of Mao. He was sentenced to two decades of hard labour. He said Hu's achievement stretched beyond the vindication campaign as he encouraged independent thinking and allowed people to have alternative views of Mao. Dai, too, was rehabilitated in 1979, thanks to Hu's efforts. "He corrected what was wrong and restored things back to order. The vindication campaign was only part of that," Dai, 86, said in a written reply to a reporter.
"At that historical juncture, if China didn't have Hu Yaobang - a leader who had the courage and spirit to say, 'If I don't go to hell, who will?'… China's 'reform and opening' would have been delayed" Dai wrote.
Li Rui, Mao's one-time secretary and a Hu ally, said Hu and his successor, Zhao Ziyang, should also be credited for their policies that allowed China's economy to flourish and granted people more social and speech freedom. If Hu and Zhao had not been toppled after their political struggles with conservatives, China would be a better, freer place today, he said.
After government critics were arrested in 1979, for allegedly spreading dissent by sharing ideas on Beijing's Democracy Wall during the "Beijing Spring", People's Daily carried an open letter by Hu saying young people should be "guided, and not suppressed or arrested", Li said.
Hu said during a speech that he hoped everyone could "enjoy the greatest freedom under the protection of the constitution".
Paramount leader Deng Xiaoping blamed Hu for condoning "bourgeois liberalisation". Hu was forced to resign from the top party post in January 1987. Officials ousted his successor, Zhao, in 1989 for sympathising with students in the Tiananmen movement.
Supporters have lamented that Hu and Zhao's steps towards political reform were abandoned. The party's fear of transparency and opposition to checks on its powers worsened corruption and social conflict and widened the income gap in the 25 years since Hu's death and Zhao's ousting, they say.
"China has never experienced a renaissance [as in the West] … and the influence of thousands of years of … [dictatorship] is just too strong," Du said.
Watch: 25 years on, China still remembers former party chairman Hu Yaobang