Li Zhisui, the late Chairman Mao's personal physician, must take an honoured place in the annals of China. Dr Li's book The Private Life of Chairman Mao painted an extraordinary full-length portrait of the tragically flawed revolutionary leader, complete with warts and feet of clay.

Li's book was published last year, almost two decades after the Great Helmsman's death. Over the intervening years, Mao's heroic reputation as a great, modernising revolutionary and a national saviour had become untenable, but it was not until the appearance of Li's scrupulously honest account that the world could view the old tyrant whole.

It was not a pretty picture. The young Zhisui Li, scion of a long line of doctors in China who wanted to be a surgeon, offered his services to the emergent People's Republic and was overcome with joy when allocated to Mao. His account of the next 22 years was a horror story, ending with the relief he felt as Mao breathed his last, a relief tortured by the fear that in the intrigue-ridden atmosphere of palace intrigue, some of those jockeying for power could accuse him of causing Mao's death.

In Mao's service, Li had been affronted by Mao's morals and his personal habits: Mao believed he could gain youthful longevity by bedding as many young women as possible, preferring unsophisticated peasant girls recruited to his entourage. He swam frequently in the swimming pool attached to his Zhongnanhai pavilion but refused to take baths - "I wash myself in the bodies of my women," he said - and infected many of them with venereal disease, for which he refused treatment. He cleaned his teeth by swilling down Chinese tea and chewing up the leaves with his greenish, plaque-covered teeth. He suffered from insomnia during periods of inactivity, but slept well when engaged in plotting the downfall of colleagues.

In his book, Li rarely moralised about his patient, recording how Mao's unrealistic belief that man's "spirit" could overcome all physical and economic impossibilities led to millions of deaths. He did record his own unease at the feasting in the Zhongnanhai during the famine in which millions died in the "bitter years" that followed the collapse of the Great Leap Forward, the creation of the Communes and the massive waste of metal and fuel in the thousands of backyard furnaces which Mao had ordained.

Li stood at Mao's elbow as he voiced neurotic suspicions of any colleague who was less than enthusiastic about his schemes or who hinted that Mao bore some responsibility for their failure. He tended Mao's ills as Mao plotted the downfall of men such as the Defence Minister Peng Dehuai or President Liu Shaoqi, who died on the floor of a miserable cell, the chief victim among millions who suffered during the destructive orgies of Mao's Cultural Revolution.

Li was horrified that China's great moderniser turned out to be as superstitious and scientifically ignorant as the Dowager Empress whose reign had also ensured that China failed to meet the challenges posed by the impact of the West.

Rarely stirring from his huge bed, immersed in novels of ancient court intrigues and biographies of the ruthless emperors in China's history he was determined to emulate, Mao became increasingly isolated from the world. Increasingly Mao saw himself as a genius thwarted by lesser men and traitors and the resulting depressions could be cured only by decisions to take action which, given his lack of reliable information and the distortions of neurosis, plunged China into crisis after crisis.

Nevertheless, and often against his conscience, Li served this monster faithfully, but at some cost. He jettisoned ambition to be a surgeon, ruined his family life and broke his wife's heart. In 1988 he managed to get to the United States where he recalled the events he had once recorded in a stack of diaries that he had been forced to burn. With the help of American scholars, he wrote them out again in a carefully unemotional, scientific style. In doing so, he dissected the heart of his tormentor and enabled posterity to judge the man who had inspired such idealistic patriotism, only to betray it.

Li Zhisui, physician: born 1920: married (two sons); died Chicago 13 February 1995.