educator and revolutionary who served as head of Peking University in Beijing from 1916 to 1926 during the critical period when that institution played a major role in the development of a new spirit of nationalism and social reform in China.

Cai passed the highest level of his civil-service examination in 1890, becoming one of the youngest successful candidates in the history of the imperial examination system. In 1904 he helped organize and became the first president of the Restoration Society (Guangfuhui), a revolutionary group dedicated to the overthrow of the Qing dynasty. Most of this group later became affiliated with the United League (Tongmenghui (Nationalist Party)), formed in 1905 by the revolutionary leader Sun Yat-sen (Sun Zhongshan), and Cai became head of the party's Shanghai branch.

As provisional president of the Chinese republic, Sun Yat-sen appointed Cai minister of education in January 1912, following the overthrow of the 2,000-year-old Chinese imperial system. Six months later, shortly after the presidency passed to the military dictator Yuan Shikai, Cai resigned his post and went to Europe, where he remained, except for a brief interval in 1913, until late in 1916. During this period, Cai organized a work-study program in which more than 2,000 Chinese students and labourers traveled to France to study in the schools and work in the factories. Many future Chinese leaders were trained in this program, including Zhou Enlai, who helped organize one of the first Chinese communist cells while in Paris.

In 1916, after first declining a position as governor of the central Chinese province of Zhejiang, Cai was made chancellor of the most prestigious school in China, Peking University. The university served as a centre of the May Fourth Movement, which began in 1919 as a student demonstration against imperialist exploitation of China and ended as a nationwide movement. Most of the future leaders of China—including the young Mao Zedong, who was employed as a clerk in the library—were associated with the university at this time.

Cai left China for Europe in 1923. In 1926 Cai went back to China and participated in revolutionary activities to support the Nationalists' Northern Expedition to unify China. After the failure of these efforts, Cai continued to work for the cause of higher education, accepting positions in Chiang Kai-shek's Nationalist government. In 1928 he helped found and served as the first president of the Academia Sinica, China's highest institution of academic study and research. In 1935 Cai resigned all official posts and retired to Shanghai.