The Pre-Socratics were not a single school but a succession of Greek thinkers who asked what the world is, how it comes to be, and what principle orders it. Thales, Anaximander, Heraclitus, Parmenides, Empedocles, the atomists, and the Pythagorean current explored nature, number, change, being, harmony, soul, and the intelligibility of the cosmos.
Their importance lies in the transition from inherited myth toward philosophical contemplation without abandoning wonder before the whole. They prepared the ground on which Plato would build, and through Plato they became part of the later Hermetic, Neoplatonic, and esoteric imagination: a cosmos ordered by logos, proportion, intelligence, and a soul capable of return.