third leader of the apocalyptic, antiforeign Tonghak (Ch'ŏndogyo) religious sect in Korea.

Born the illegitimate son of a low-echelon government official, Son grew up in poverty, suffering much discrimination. In 1897 he was elected to the leadership of Tonghak, succeeding Ch'oe Si-hyŏng, and he successfully reconstructed the sect, which had been hurt by the failure of its uprising in 1894.

Branded a political criminal by the state, he went into exile in Japan. When Korea lost its sovereignty to Japan in 1905, he renamed the Tonghak sect the Ch'ŏndogyo (q.v.; literally “Religion of the Heavenly Way”) and set about reorganizing it as a genuine religion. He undertook educational and cultural projects, running or supporting schools, conducting enlightenment programs for Ch'ŏndogyo followers, and leading campaigns for constructive living. In 1919 he led the nationwide movement for Korean independence.