What does the term alien refer to in the concept of alienation? Do you find this concept plausible?

Karl Marx was an extremely influential character within the world of political theory and his theories and attitudes towards capitalism undoubtedly had a massive impact upon humankind. Among his many influential ideas and criticisms of capitalism, one of the most central themes in Marxs writings was the concept of alienation.

The exact concept of alienation was rather complex and took several different forms that were based upon one fundamental principle. The essence of this principle lies in the problem that man creates conditions and is then subsequently ruled by these conditions. This notion of alienation came most directly from Hegel, yet Marx criticised Hegels view on alienation….(short extract)