Social contract is a concept in political philosophy as a justification for the existence of state, or government, by the consent of the people among themselves and/or with the governing authority, in a collective agreement analogically called "contract". One of the earliest proponent of social contract theory was Thomas Hobbes, who espoused monarchical absolutism. However, the concept was then used by different theorists such as John Locke, Jean-Jacques Rousseau and Immanuel Kant to arrive to their conclusion supporting different forms of liberal or democratic state.
In the modern era, social contract was revived again by modern American philosopher John Rawls. Greatly influenced by the Kantian version of social contract, Rawls rebranded it into his own version and named it "original position" in his A Theory of Justice.
Thomas Hobbes (1588-1679), a British political philosopher who lived during the British Civil War, propounded his theory concerning political legitimacy of the state in the book Leviathan. To Hobbes, humans are inherently selfish and with unlimited greed, restrained only by the fear of death. If left without a state, state of nature would ensue, which is "war of every man against every man", or, in another word, bloody chaos. To avoid such "war", humans made agreement with each other to conceive an agent, the sovereign, to maintain order and to protect the safety of men. This sovereign himself is not a party of social contract, but only a result of the contract between every man. Therefore, the sovereign is an absolutist monarch with no limitation to his authority.
John Rawls' "original position"
British utilitarian philosopher John Stuart Mill rejected the social contract theory. In the fourth chapter of On Liberty, Mill wrote that "society is not founded on a contract ... no good purpose is answered by inventing a contract in order to deduce social obligations from it".