Heraclitus was an ancient Greek pre-Socratic philosopher from the city of Ephesus, which was then part of the Persian Empire. He exerts a wide influence on ancient and modern Western philosophy, through the works of authors such as Plato, Aristotle, Hegel, and Heidegger.
Little is known of Heraclitus's life. He wrote a single work, only fragments of which have survived, catalogued under philosopher number 22 in the Diels–Kranz numbering system. Even in ancient times, his paradoxical philosophy, appreciation for wordplay, and cryptic, oracular epigrams earned him the epithets "the dark" and "the obscure". He was considered arrogant and depressed, a misanthrope who was subject to melancholia. Consequently, he became known as "the weeping philosopher" in contrast to the ancient atomist philosopher Democritus, who was known as "the laughing philosopher".
The central ideas of Heraclitus's philosophy are the unity of opposites and the concept of change. Heraclitus saw harmony and justice in strife. He viewed the world as constantly in flux, always "becoming" but never "being". He expressed this in sayings like "Everything flows" and "No man ever steps in the same river twice".