Xenophanes was a Pre-Socratic philosopher who criticized the human-like portrayal of gods in Greek mythology and proposed a more abstract, monotheistic view of divinity. He emphasized skepticism and the limitations of human knowledge. Heraclitus, another Pre-Socratic philosopher, introduced the idea of constant change or "everything flows." He believed that opposing forces were necessary for maintaining harmony and that a rational principle called "logos" governed the universe. Heraclitus also explored questions about the nature of knowledge and reality. Their ideas greatly influenced ancient Greek philosophy and subsequent philosophical thought