Euthyphro of Prospalta, and Socrates are best know by the writings of who?
Euthyphro (prophet):  400 BCE) was an ancient Athenian religious prophet ("mantis") best known for his role in his eponymous dialogue written by the philosopher Plato. Socrates:  He is an enigmatic figure known chiefly through the accounts of classical writers, especially the writings of his students Plato and Xenophon and the plays of his contemporary Aristophanes.
Plato