Chaerephon (born ca. 470-450 BC, died ca. 405-399 BC), of the Athenian deme Sphettus, was a loyal friend and follower of Socrates. He is mentioned by three writers of the time, all of whom probably knew him: Xenophon, Aristophanes, and Plato.

In his Memorabilia Xenophon includes Chaerephon in his list of the "true companions" of Socrates. Also in the Socratic inner circle, according to Xenophon, were Crito, Hermogenes, Simmias of Thebes, Cebes of Thebes, Phaedondes, and Chaerephon's younger brother Chaerecrates (and Xenophon acknowledges that there were others). Later in the Memorabilia, Xenophon recounts an exchange between Socrates and Chaerecrates on the occasion of a falling-out between the brothers. Socrates argues persuasively that Chaerecrates should make every effort to achieve a prompt reconciliation with his older brother Chaerephon.

Chaerephon appears in three of Aristophanes' comic plays: The Clouds, The Wasps, and The Birds. The Clouds (produced in 423 BC) portrays Socrates and his assistant Chaerephon as a pair of charlatans operating a pseudo-scientific school in Athens. Chaerephon is represented in The Clouds as pale and malnourished, a "living corpse," and it is sometimes inferred that he must have been a thin, unhealthy looking fellow in real life. In The Wasps Chaerephon (or some visual caricature of him) has a brief, non-speaking role as an impartial witness. In The Birds he is nicknamed "the bat," possibly alluding to nocturnal habits, a bony appearance, or a sudden, excitable nature (as suggested in Plato's works, below).

In Plato's Apology, which is an account of the Trial of Socrates (in 399 BC), Socrates calls Chaerephon his longtime friend and the friend of many present. Socrates tells us that Chaerephon is now deceased but indicates that his brother is in attendance at the trial. Socrates suggests that Chaerephon had a reputation for being impetuous and we learn that it was Chaerephon who journeyed to Delphi to ask the Delphic Sibyl who was the wisest of men. (The oracle replied that there was none wiser than Socrates.) Socrates also alludes to a period of exile which was endured by Chaerephon and some others present. This is sometimes taken as evidence that Chaerephon (unlike Socrates) was an active supporter of the Athenian Democracy and was persecuted on this account when the democracy was temporarily deposed after the defeat of Athens by Sparta.

Chaerephon appears in two other Platonic dialogues: the Cha'rmides and the Gorgias. At the start of the Charmides Socrates returns to Athens from the military campaign at Potidaea and is greeted with great enthusiasm by Chaerephon who is described as "a wild man." This campaign concluded in 430 BC (3 years before Plato's birth and 31 years before Socrates' death), but Plato is probably accurate in depicting the association of Chaerephon and Socrates as already well established. At the start of the Gorgias, Chaerephon and Socrates arrive late at an Athenian gathering for an evening of conversation with Gorgias, a famed Sophist. Socrates good-naturedly blames their lateness on Chaerephon, who chatted too long in the Agora. Chaerephon then says that Gorgias is a friend of his and, with some coaching by Socrates, he serves satisfactorily as Gorgias' initial interlocutor in the early part of the dialogue.

Considered together, these sources suggest that Chaerephon was a well-known, alert, energetic, engaging individual, possibly with a distinctive physical appearance and probably a bit of a "character," who moved easily in the social and intellectual circles of the day.