Katayama, Tetsu (tĕtˈsŏ kätäyäˈmä) [key], 1887–1978, Japanese statesman. He was a founder (1926) of the Social Democratic party. When the party was suppressed by the police, Katayama helped organize (1931) its successor, the Social Mass party. He was forced to retire from prewar politics because of his opposition to the Manchurian Incident. After World War II he reentered politics as president of the Socialist party and was prime minister (1947–48) of a coalition cabinet.