Heraclitus was born in roughly 540 to an aristocratic family in Esphesus. Heraclitus disliked the political life typically pursued by those of his stature and passed on his right to a hereditary ruling position to his brother. Heraclitus had a reputation for misanthropy and obscurity which gave him the nickname "The Riddler".
Heraclitus' greatest contribution was the argument that there is a single divine law of the universe which he called logos.
Logos was defined as "thing said","account", "word" or "rational principle". Heraclitus argued the differences between divine knowledge (objective truth available to all) and human knowledge (the collection of facts). Heraclitus' arguments about logos were to confirm that everything that is known shares an underlying unity. Despite the fact that the universe is changing, there is a single, unchanging law of the cosmos, A logos which joins and governs these changes.
Thus the physical manifestation of logos was fire, an elemental symbol that is in constant flux yet always the same.