Stevens, Siaka Probyn (sēäˈkä prōˈbĭn) [key], 1905–88, president of Sierra Leone (1971–85). He served (1951–57) in the legislative council and was appointed (1967) prime minister. Briefly exiled, he returned as prime minister (1968–71). In 1971 he became president under a new constitution that established a republic. Stevens established a one-party state in 1978. In 1985 he retired and was succeeded by Major Gen. Joseph Momoh.