Heraclitus, was in his floruit around 500 BC. He was an ancient Greek pre-Socratic philosopher.
Little is known about Heraclitus's life. He regarded himself as self-taught.
We can summarize his philosophy by saying all things come into being by conflict of opposites and that the sum of all things flow like a stream.
As his predecessors dealt with the arche, for example, that Thales said it was water, Anaximander said it was apeiron and Anaximenes said it was air. Heraclitus, will thus hold it to be fire. Fire was the fundamental element that gave way to the other elements. This is perhaps, because, living people are warm. Other scholars see this as a metaphor for change. There has also been speculations of Zoroastrian influence with their concept of Atar, a holy fire.
Perhaps the most familiar of Heraclitus's sayings is "everything flows." Few modern scholars think he said this. Since the time of Plato, Heraclitus's theory of flux has been associated with a flowing river.
Heraclitus said that "It is not possible to step into the same river twice."