Pherecydes of Syros was an early Greek thinker from the island of Syros, active in the 6th century BCE. He is considered one of the first philosophers and a foundational figure of the pre-Socratic tradition. Ancient sources sometimes name him as a teacher of Pythagoras, though the historicity of this connection is uncertain. He is distinguished from a later Athenian writer of the same name.

His primary work was a prose cosmogony titled Heptamychos or Theology, which survives only in fragments. The title, meaning "Seven Recesses," may refer to the structure of the cosmos described in the book. With this work, Pherecydes holds a pivotal place in Greek intellectual history as one of the very first authors to write in prose, moving away from the poetic tradition of Homer and Hesiod to articulate new ideas about the world's origins.

His significance lies in this transitional role between myth and philosophy. His system introduced novel theological elements, featuring eternal primal deities like Zas (Zeus), Chronos (Time), and Chthonie (Earth), and using the concept of a divine marriage to explain the creation of the cosmos. According to modern scholars, while his ideas remained deeply theological, his systematic, prose approach to explaining the universe's origins influenced later philosophical and cosmological thought.