Victorian Web
Brown University: Victorian Web: Karl Marx (1818 1883)
This site provides a detailed biography of Karl Marx. Links to related essays and articles are provided within The Victorian Web. This article is somewhat brief but provides good information on the subject.
Purdue University
"Terms Used by Marxism." Introductory Guide to Critical Theory, by Dino Feluga
Marxist terms that are presented in alphabetical order; however, someone beginning to learn Marxism and neo-Marxism needs to stay conscious of the fact that each major theorist uses particular terms in his or her particular way.
Wikimedia
Wikipedia: Proletariat
Wikipedia offers the definition of the Proletariat, the working class as defined by the Romans and by in Marxist theory.