Ernest Mandel was a revolutionary Marxist theorist. After WWII, he became a leader of the Belgian Trotskyists and the youngest member of the Fourth International secretariat. He gained respect as a prolific journalist with a clear and lively style, as an orthodox Marxist theoretician, and as a talented debater. 

In his writings, perhaps most striking is the tension between creative independent thinking and the desire for a strict adherence to Marxist doctrinal orthodoxy. It was in the 1960s that Mandel became world renown as a leading Marxist economist and political analyst. His seminal works, Marxist Economic Theory, was first published in 1962, Late Capitalism in 1978, The Long Waves of Capitalist Development, and The Second Slump, both in 1980, right up to his latest works, Power and Money, 1992, and Trotsky as Alternative, 1995, continue to have major influence on activists, radical intellectuals and academics the world over. Mandel's Introduction to Marxist Economic Theory, a small book based on lectures published in 1967, has a circulation of more than two million copies in about a dozen languages.

Ernest Mandel internet archive in English
http://www.ernestmandel.org/en/index.html

Speech by Ernest Mandel: Self Management - dangers and possibilities