(James Riddle) (1913-1975) Notorious US labor union leader. A member of the Teamsters' (trucking) Union since 1931, he became its ruthless president 1957. In 1964 he effected the first national contract for the truckers but was also convicted in two trials of fraud and jury tampering. He went to prison 1967 and retained his presidency until 1971, when President Nixon commuted his sentence on condition that he should not engage in union activity until 1980. Hoffa disappeared 1975, however, and is considered to have been murdered.