Plato (ca. 428–348 BC) was an Athenian philosopher. He was born to a wealthy and powerful family and demonstrated an early talent as a writer. Falling under the spell of Socrates, an older philosopher who left no writings but was much admired by many followers, Plato turned his attention from literary pursuits to philosophy and founded the Academy, a gathering place dedicated to the Muses where those interested in philosophy could gather, share ideas, and study.

Although its precise date is unknown, Euthyphro is usually categorized among Plato's "early" dialogues and presumed to have been written shortly after the death of Socrates in 399 BC. The main characters in the dialogue are:

• Socrates: a philosopher whom Plato very much admired
• Euthyphro: a self-proclaimed religious authority accusing his father of murder in a lawsuit
• Meletus: a man who would later accuse Socrates of impiety in a trial resulting in Socrates' death

The main theme of Euthyphro is the nature of piety and whether things are considered pious because they are approved by the gods or whether the gods approve of things because those things (ideas, behaviors) are inherently good or pious in nature. An important issue in the dialogue is the question not just of what is a good definition of piety but the more general issue of what constitutes a good definition.