Heraclitus

Ancient Greek pre-Socratic philosopher — known as 'the Obscure' — author of the fragments containing his doctrine of universal flux, the unity of opposites, and the Logos — whose ideas influenced Stoicism and (through John's Gospel) Christianity.

Creates the doctrine of universal flux and the Logos concept — Heraclitus's core claim (that change is the fundamental nature of reality; that opposites are united; that there is a rational principle, the Logos, underlying all change) is the most influential pre-Socratic contribution to Western philosophy; the Logos concept directly influenced Stoicism and through John's Gospel ('In the beginning was the Logos') became foundational to Christian theology.