Socrates was an influential philosopher in ancient Athens who used questioning to challenge beliefs and was ultimately sentenced to death. Plato was Socrates' student and founded his own philosophical Academy. He believed in forms/ideas and advocated for a society ruled by philosopher kings. Aristotle was Plato's most famous student, tutored Alexander the Great, and founded his own school. He emphasized happiness and reason. After Aristotle, Greek philosophy declined due to political changes but schools like the Stoics and Epicureans emerged focusing on ethics and practical life issues. Philosophy became more eclectic and cosmopolitan.