Anaximander was a pre-Socratic Greek philosopher who lived around 610-546 BCE. He is best known for his work in cosmology, geography, and biology. Anaximander proposed that the fundamental substance of the universe is the apeiron, or the "infinite," which he believed to be an eternal and boundless source from which all things arise and to which they return. In addition to his philosophical contributions, Anaximander is credited with creating one of the earliest maps of the known world and developing a theory of evolution, suggesting that humans evolved from fish-like creatures. His ideas laid the groundwork for later philosophers, including Aristotle and Plato.