Plato
en.wikipedia.org
Plato
these ancient philosophers did not keep their discoveries to themselves or share them only with their fellow philosophers. Rather, they formed schools and welcomed as their pupils anyone wishing to acquire a philosophy of life. Different schools offered different advice on what people must do in order to have a good life.
William B. Irvine • A Guide to the Good Life: The Ancient Art of Stoic Joy
Aristotle’s metaphysics, roughly speaking, may be described as Plato diluted by common sense.
Bertrand Russell • History of Western Philosophy
Plato and his students were not narrow specialists, not pedants, not ideologues; they were rather propelled to dispute, to discover, everything there was to know, and to test the boundaries of knowing itself.