Okay, so I'm going to take a guy who, when you think about it, has caused the Americans fits for over a century and a half now...
Karl Marx. He'll take up my philosophizing (holy crap I can't believe that's an actual word) spot.
Although he probably wouldn't consider himself a Marxist nowadays, he set into motion the entire communist system. I still think it's possible for a good communist system to work, but it'd take a tonne of retooling. If it worked as well in practice as it did in theory, it'd be a great, great system. Anyways, stuff on Marx:
Oh, one more thing...he had one of the greatest beards ever.
Marx distinguished historical eras in terms of distinct modes of production. For example, he observed that European societies had progressed from a feudal mode of production to a capitalist mode of production. Marx believed that under capitalism, the means of production change more rapidly than the relations of production (for example, we develop a new technology, such as the Internet, and only later do we develop laws to regulate that technology). Marx regarded this mismatch between (economic) base and (social) superstructure as a major source of social disruption and conflict.
As a scientist and materialist, Marx did not understand classes as purely subjective (in other words, groups of people who consciously identified with one another). He sought to define classes in terms of objective criteria, such as their access to resources — that is, whether or not a group owns the means of production. For Marx:
Marx argued that this alienation of human work (and resulting commodity fetishism) functions precisely as the defining feature of capitalism. Prior to capitalism, markets existed in Europe where producers and merchants bought and sold commodities. According to Marx, a capitalist mode of production developed in Europe when labor itself became a commodity—when peasants became free to sell their own labor-power, and needed to do so because they no longer possessed their own land. People sell their labor-power when they accept compensation in return for whatever work they do in a given period of time (in other words, they do not sell the product of their labor, but their capacity to work). In return for selling their labor-power they receive money, which allows them to survive. Those who must sell their labor-power are "proletarians". The person who buys the labor power, generally someone who does own the land and technology to produce, is a "capitalist" or "bourgeois". The proletarians inevitably outnumber the capitalists.
The work of Marx and Engels covers a wide range of topics and presents a complex analysis of history and society in terms of class relations. Followers of Marx and Engels have drawn on this work to propose grand, cohesive theoretical outlooks dubbed "Marxism". Nevertheless, Marxists have frequently debated amongst themselves over how to interpret Marx's writings and how to apply his concepts to their contemporary events and conditions. Moreover, one should distinguish between "Marxism" and "what Marx believed"; for example, shortly before he died in 1883, Marx wrote a letter to the French workers' leader Jules Guesde, and to his own son-in-law Paul Lafargue, accusing them of "revolutionary phrase-mongering" and of lack of faith in the working class. After the French party split into a reformist and revolutionary party, some accused Guesde (leader of the latter) of taking orders from Marx; Marx remarked to Lafargue, "if that is Marxism, then I am not a Marxist" (in a letter to Engels, Marx later accused Guesde of being a "Bakuninist").