G.W.F. Hegel (1770-1831) is a German philosopher whose work has been very influential among many social theorists who followed him. He developed a philosophical system that looks at the development of reason which interprets reality through a dialectic method.  Some of his most influential concepts include sublation, self-consciousness, contradictions, "Spirit", dialectic, etc. which are further explained in his piece on the "Master/Slave" dialectic, which is an excerpt from one of his most important philosophical works, The Phenomenology of Mind. 

To briefly summarize, Hegel believes that within all relationships, which are seen as a unity of opposites, there exists contradictions, which are in fact the force of change. Through its development, self-consciousness dialectically sublates into a higher unity of reason and self consciousness of humankind, and through long-term historical development humanity achieves a state of knowledge that is not divided against itself. He believes that the whole process towards the end product of Absolute Knowledge (i.e. Spirit, Geist, etc.) is a slow process of struggle and conflict, where an internal and external other continue to sublate one another until there is unification. 

Hegel believes the self is composed of multiple forces (self and other) which cannot exist without recognition from an outside "Other". These selfs are in a constant state of sublation. Sublation means to eliminate, and the elevate.  Hegels uses this idea in conjuction with his theory that is self is composed of multiple forces. With every new relationship, every new growth, a part of your self is lost, and another is gained. This process occures over and over, with the ultimate goal being Absolute Knowledge... and....

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In many ways Hegel's theories are a response to most of the social and political theoriest that came before him in the Enlightenment. He posits that "reason" is neither immediate or mediated, that the formation of all relationships and societal forms are a process, and that there is no state of nature to foil our society or the psyches of individuals against.