St. Thomas Aquinas-heavily influences my belief in God; from a philisophical standpoint and not a religious standpoint.
Locke influences my politics in a basic way, but I don't know much about him.
If you want to call him one like opebo does, Sigmund Freud. Freud is too highly ridiculed by the modern media as a 'sexist pig', but he did contribute a lot to psychology and he is right about a great many things.
Socrates-because his method of questioning everything makes the world more understandable in a specific sense.
And finally, Rene' Descarte, for making me look at the world in a really weird way. Ex-I cannot prove this computer I'm typing on exists, yet I can because my thoughts confirm my existence.
Add to list Ayn Rand, Aristotle, Locke, deTocqueville