Philosopher-kings strive to lead individuals out of the cave, and to perceive 'the real,' the pure and ideal world of the forms rather than the shadows of ideals. This idealistic concept is one reason why Plato is so determined that every human being assume his ideal place in the social order, whether working at a trade, fighting, or engaging in philosophy. While Plato's version of a social contract between the different classes of society is, in his view, a mutually beneficial one, in Hobbes' view the social contract between sovereign in subjects is unequal, but extremely necessary because life is not worth living without such a contract. If there is any part of Plato that Hobbes would agree with, it is the "Myth of Gyges" which is told by an opponent of Socrates, the advocate of tyranny Glaucon (a kind of precursor to Hobbes). Gyges was a shepherd who became invisible when he put on a ring, and although he was moral before, he engaged in unspeakable brutalities, simply because he could do so without consequences and became king (Bernard 1996). The social contract creates protections for those who cannot fight back, and makes...

We are all Gyges in Hobbes' view, because we will all take advantage of a situation to suit our own self-interest. So long as someone may sleep, they may be killed. This is also why Hobbes preferred a single sovereign, as opposed to even a sovereign governing body like Parliament or Plato's oligarchy of philosopher-kings (Williams 2006). The stronger the individual, the more he was likely to preserve order -- although, one could add, the more likely the sovereign was apt to abuse his power, in the absence of constraints.
Works Cited

Bernard, Suzanne. "The Ring of Gyges." Plato's Republic. 1996. Last updated

November 22, 1998. April 18, 2009.

http://plato-dialogues.org/tetra_4/republic/gyges.htm

Hobbes, Thomas. Leviathan. New York: Penguin Classics, 1968.

Plato. The Republic. April 18, 2009. http://classics.mit.edu/Plato/republic.html

Williams, Gareth. "Thomas Hobbes." Internet Encyclopedia of Philosophy. 2006.

April 18, 2009. http://www.iep.utm.edu/h/hobmoral.htm#H5