Who is Thomas Hobbes and why is he a notable philosopher? What philosophical ideas influenced him?

Thomas Hobbes (1588-1679) is one of the most influential moral and political philosophers of the early modern period.  His most famous work, Leviathan (1651) most clearly and thoroughly elaborates his ideas concerning the nature of society and the role of government in the success of a society.  In addition, he made significant contributions to the realms of epistemology (theories of knowledge) and metaphysics.  He is notable because, like very few of his contemporaries (Descartes may be an exception), he is able to synthesize these different philosophical strands into a consistent system.

Hobbes begins his argument by suggesting man seeks his pleasure above all else.  In his most primitive state, the state of nature, man could pursue his savage egoism without any recourse to others; however, with the formation of societies, man's egoism must be steered by an external body, a government, especially since war would be continual and an unavoidable consequence without a governing institution.  A governing body ensures peace, and in doing so allows for the pursuit of maximum pleasure.  To accomplish this, commoners in society cede their natural rights to an absolutist ruler.  Hobbes's line of argument says a great deal about how he views human nature.  Humanity needs to be guided by an absolute monarch; without such a monarch's guidance, the maximum good for society cannot be realized.

Beyond his political ideas, Hobbes has very clear perspectives on epistemology, which for his rests in a combination of empiricism and rationalism.  His theory of knowledge derives a great deal from the nominalism he had learned while at Oxford.  Empiricism is important for an understanding of society, but it is the rational faculty that develops the elements of experience.  The concepts devised in the process do not have an explicit connection with the external world, but they do serve to describe the world well.

Hobbes's ideas have varied origins.  His nominalism, the idea that the concepts of the mind (including language) do not have more than a descriptive connection with the external world, comes straight out of the late Middle Ages - particularly the philosophy of famous Oxford scholars such as Duns Scotus and William of Ockham.  Hobbes's political ideas spring from the political ideas of the Renaissance and early modern period.  Like Hobbes, Machiavelli indicates the need for an absolutist ruler to ensure society's success.

In his metaphysical thought, he follows much of Descartes's ideas concerning extension - at least the extension of material substance.  Unlike Descartes, Hobbes endows matter with motion.  It is active rather than passive.  This idea has much more in common with Aristotelian thought (potentiality v. actuality), which he would have learned at Oxford.  For Aristotle, matter has the potential to move, though it does not mean that it will actualize that potential.  It is a purely internal view of the material world.  External forces are not the motivating factors.