Karl Marx - Marxism

http://www.jahsonic.com/Marx.html

Many of his ideas were reintroduced in the 20th century starting with sociology, then with other critical theories.  His ideas were influential to many post-modern thinkers.

Marx was a materialist

http://www.awerty.com/das2.html

In Das Kapital, Marx describes the problems and pitfalls of capitalism that would lead to its failure.

Critical Theorists, especially those in the Frankfurt school, took Marxism and 're-applied' it to modern problems.  They focused on Marx's equality and hegemony principles in neo-Marxism, and less on Marx's ideas about the failure of capitalism.

Marx and Mass Media:  http://www.marxismmadesimple.esmartweb.com/massmedia.htm