Karl Marx would be one. His influence on writers, academics, intellectuals and educators and society, in general, by him has been profound. The power of his ideas has changed the way we look at the world. He was critical of social conditions and existing political arrangements. His radicalism came to be recognized as 'communistic'. Every college student must be aware of Marx and his ideas. Today, we have Marxist anthropology, Marxist literary criticism, Marxist aesthetics, Marxist pedagogy, Marxist cultural studies, Marxist sociology etc. At the cornerstone of his thinking is the concept of the class struggle. How many of us do not talk about upper class, middle class, and lower class? He didn't discover the existence of class, but he helped us to understand and change them. He brought forward "class struggle" and the idea that there should be a classless society. The political system, the legal system, the family, the press, the education system were all had ideas rooted in class and continue to be influenced by Marx's works and those that followed him. For a list of "Who Was Influenced By Karl Marx" see http://www.freebase.com/view/guid/9202a8c04000641f80000000085df3ac