On May 3, just two days before the 200th anniversary of Karl Marx's birth, Zheng Derong, an expert in the history of the Communist Party of China (CPC), died at age 92.

He was planning to participate in a theoretical seminar that was being held in Beijing to mark the auspicious anniversary.

Just several days before he passed away, he pulled out his oxygen tube and with the help of his doctoral student, insisted on polishing his thesis for the seminar in his hospital bed.

It took his student Hu Fankun two hours to finish reading the paper to him and Zheng, barely able to speak, simply made some suggestions on the structure of the piece.

According to Wang Chunyan, one of his doctors, he refused to take painkillers until the pain was unbearable in order to keep a clear head.

His thesis for the seminar covered the localization of Marxism in China, dealing with its process, achievements and experience.

As an emeritus professor at the Northeast Normal University in Changchun, Northeast China's Jilin province, Zheng had been researching the history of the CPC for 67 years.

Since graduating from the university in 1952, he published dozens of academic books and more than 260 papers in professional journals and Party newspapers.

Some of his work has even found a home in the Library of Congress and Harvard Library in the US.

Zheng was also one of the earliest Chinese historians to systematically study Mao Zedong Thought. He argued that Mao was the initiator of adapting Marxism into a Chinese context, and that Mao Zedong Thought is rooted in both Marxism and the traditional Chinese culture.

According to Wang Zhanren, one of his doctoral students and a professor at the university, Zheng had been instrumental in drawing up the vital document which was adopted at the Sixth Plenary Session of the Eleventh Central Committee of the CPC in June 1981.

The document helped to repudiate the "cultural revolution" (1966-76), clarify Mao's merits and faults, and discussed the substance of Mao Zedong Thought and its historical role.

Zheng worked for the Party History Research Office from 1980 to 1982, where he participated in the editing of the chronology of major events in the history of the CPC, with a focus on the Agrarian Revolutionary War (1927-37), during which Mao Zedong Thought was formed.

He also proved some of the controversial facts of the time and his correction was recognized by Hu Qiaomu, director of the office at that time.

From the perspective of combining Marxism with China's reality, Zheng demonstrated that Mao Zedong Thought and Deng Xiaoping Theory developed in one continuous line.

Around 2008, questions were asked why Mao Zedong Thought, unlike Deng Xiaoping Theory, the Theory of Three Represents and the later Scientific Outlook on Development, was not included in the theoretical system of socialism with Chinese characteristics, which mainly focuses on socialist construction rather than revolution.

In order to clear up the confusion, Zheng wrote to interpret the relations between Mao Zedong Thought and the theoretical system of socialism with Chinese characteristics, explaining the value of Mao's thought legacy, while pointing out that not being included in the latter didn't diminish Mao Zedong Thought.

"People's understanding and attitude about historical events, consciously or unconsciously, is limited by the times. There is great space for the research of history of the Party, which requires constant exploration and innovation and we should keep pace with the time," Zheng once said.