Slovak lawyer, political journalist, and communist politician.

In 1942 Clementis was appointed by President Edvard Beneš to the Czechoslovak National Council in exile (headquartered in London). After the liberation of Czechoslovakia from the Germans at the end of World War II, he became possibly the strongest figure in Jan Masaryk's (Masaryk, Jan (Garrigue)) foreign ministry, and he succeeded to the foreign secretaryship following Masaryk's murder or suicide in 1948. Officially disgraced in 1950 for his allegedly insufficient Stalinism, he was convicted in 1952 on charges of treason and espionage and was sentenced to death.