Kernel
Aristotle is the figure who systematizes Greek thought into a curriculum. The Lyceum's lectures cover physics, biology, ethics, politics, rhetoric, and the formal logic that becomes the operating syntax of Western reasoning for two thousand years. He is also the tutor of Alexander the Great, whose imperial expansion will fund the Library of Alexandria — the institution that preserves much of his work for posterity.
Contribution
Formal logic (syllogism), the principle of non-contradiction, the empirical method in zoology, four-cause analysis (material/formal/efficient/final), the Politics's classification of regimes. The corpus runs to roughly a million words and frames every subsequent Western philosophical tradition either by extending it or rebelling against it.
Lineage
Mentored by Plato (Plato by Socrates). Tutored Alexander. His texts re-emerge in medieval Europe through Arabic translations made in Baghdad and re-Latinized in Toledo and Bologna in the 12th–13th centuries. Aquinas reconciles him with Christianity. Galileo argues against him; Newton, in part, replaces him.
Civilization-scale significance
The single figure whose vocabulary the West argues with for the longest time. Most undergraduate philosophy is still organized around "things Aristotle said and things people said in response."