Which philosopher is known for believing that the physis of the universe is fire?

Heraclitus is renowned for his belief that fire is the fundamental essence or "physis" of the universe. This concept is rooted in his broader philosophical view that all things are in a state of constant change and flux, expressed in the famous maxim "everything flows" ("panta rhei"). He saw fire not only as a physical element but also as a symbol of transformation and the continual process of becoming. This perspective reflects Heraclitus's belief in the unity of opposites—suggesting that just as fire consumes and transforms, so too does life encompass a constant interplay of creation and destruction. This philosophical stance distinguishes him from other thinkers, who might attribute the essence of the universe to concepts such as unchangeable forms (as seen in Platonic thought) or elemental combinations (as proposed by Aristotle and Democritus).