Who was the ancient Greek philosopher who taught Alexander the Great?

Aristotle, hired by Philip II to tutor his son for several years from about 343 BC - a chain that runs Socrates to Plato to Aristotle to Alexander, which is an unreasonable concentration of consequence in four lifetimes.

What Alexander took from it is arguable. He carried a copy of the Iliad annotated by Aristotle on campaign and sent biological specimens back from Asia, which suggests the interest was real. He also killed close friends in rages and had Aristotle's nephew Callisthenes executed, which suggests the moral philosophy took less well.

Aristotle's own influence is harder to overstate and was not uniformly good. He effectively invented formal logic, systematic biology and the practice of classifying knowledge into disciplines, and his zoological observations were good enough that some were only confirmed in the twentieth century. But his physics was wrong in ways that mattered - heavier objects fall faster, motion requires continuous force - and because medieval Europe treated him as the authority, those errors held for the better part of two thousand years. Being right about a great deal and revered for all of it turned out to be a poor combination.