Back in the day... I remember it well. I conceived of these petty ideas you mere mortals have taken to naming silly things like epistemology, ontology and the mind-body problem. I thought up everything a human could possibly think up. I've also taken on a few aliases over the years, Descartes, Socrates, Plato, just to name a few.
Aristotle believed that truth resided in the world around us. This man was methodical and down to earth. With his philosophical approach. He gathered knowledge empirically, which laid the foundation for modern science, where knowledge is based on observations and experiments in the labs. Aristotle also laid the foundation for logic.
No one could be the greatest, especially of all time, because no one can know all details of this world. I believe that the greatest always stays behind the scene that many can feel the power of his efforts but never realize his existence. Indeed, the great work of Plate, Socrates, Nietzsche and etc. Cannot be denied, but their work never appear independently and be isolated from others, there are links among every of them and every time. So, How could we know? We never know the answer as we never can hold the truth tight but can only chasing behind it as closely as we could.