Plato

An Athenian of good family who watched the city he was born to lose a war, try tyranny, restore its democracy, and then execute his teacher — and who spent the rest of his life asking what a just city would have to be like, and what kind of person could be trusted to run one. He founded the Academy, taught for forty years, and wrote almost everything as dialogue, so that no sentence in the corpus is straightforwardly his.

The headwater of the entire kindred-ways annex. Four words of his — the Good is "beyond being" — become Plotinus's One, and by a documented route become Ein Sof. Everything else on these benches is downstream of a conversation he set at a dinner party.