Ernest Ezra Mandel, also known by various pseudonyms such as Ernest Germain, Pierre Gousset, Henri Vallin, Walter etc. (b. Frankfurt April 5, 1923 - d. Brussels July 20, 1995). He was recruited to the Belgian section of the Fourth International in his youth in Antwerp. His parents, Henri and Rosa Mandel, were a Jewish emigres from Poland, the former a member of Rosa Luxemburg's and Karl Liebknecht's Spartacist League. Ernest's entrance to university studies was cut short when the German occupying forces closed the university down.

During World War II, he escaped twice after being arrested in the course of resistance activities, and survived imprisonment in the German concentration camp at Dora. After the war, he became a leader of both the Belgian Trotskyists and the youngest member of the Fourth International secretariat, alongside Michel Pablo and others. He gained respect as a prolific journalist with a clear and lively style, as an orthodox Marxist theoretician, and as a talented debater. He wrote for numerous media outlets in the 1940s and 1950s including Het Parool, Le Peuple, l'Observateur and Agence France-Presse. At the height of the Cold War he publicly defended the merits of Marxism in debate with the social democrat and future Dutch premier Joop den Uyl.

After 1946 World Congress of the Fourth International, Mandel was elected into the leadership of the International Secretariat of the Fourth International. In line with its policy, he joined the Belgian Socialist Party where he was a leader of a militant socialist tendency, becoming editor of the socialist newspaper La Gauche (and writing for its Flemish sister publication, Links), a member of the economic studies commission of the General Confederation of Labour of Belgium and an associate of the Belgian syndicalist André Renard. He and his comrades were expelled from the Socialist Party not long after the Belgian General Strike for opposing its coalition with the Christian Socialists, and its acceptance of anti-strike legislation.