You can vote for the greatest philosopher of all time here, from a shortlist of 20. It's a tough business. I'll give you my own shortlist from the shortlist - from which I'll have to make up my mind. In alphabetical order:
Thomas HobbesThis isn't strictly relevant. And before anybody starts moaning at me, I've done my shortlist on a 'favourites' basis.
David Hume
Immanuel Kant
Karl Marx
John Stuart Mill