In Greek and Roman mythology, Apollo (in Greek, Ἀπόλλων—Apóllōn or Ἀπέλλων—Apellōn), is one of the most important and many-sided of the Olympian deities. The ideal of the kouros (a beardless youth), Apollo has been variously recognized as a god of light and the sun; truth and prophecy; archery; medicine and healing; music, poetry, and the arts; and more. Apollo is the son of Zeus and Leto, and has a twin sister, the chaste huntress Artemis. Apollo is known in Greek-influenced Etruscan mythology as Apulu. Apollo was worshipped in both ancient Greek and Roman religion, as well as in the modern Hellenic neopaganism.

As the patron of Delphi (Pythian Apollo), Apollo was an oracular god — the prophetic deity of the Delphic Oracle. Medicine and healing were associated with Apollo, whether through the god himself or mediated through his son Asclepius. Apollo was also seen as a god who could bring ill-health and deadly plague as well as one who had the ability to cure. Amongst the god's custodial charges, Apollo became associated with dominion over colonists, and as the patron defender of herds and flocks. As the leader of the Muses (Apollon Musagetes) and director of their choir, Apollo functioned as the patron god of music and poetry. Hermes created the lyre for him, and the instrument became a common attribute of Apollo. Hymns sung to Apollo were called paeans.

In Hellenistic times, especially during the third century BCE, as Apollo Helios he became identified among Greeks with Helios, god of the sun, and his sister Artemis similarly equated with Selene, goddess of the moon. In Latin texts, however, Joseph Fontenrose declared himself unable to find any conflation of Apollo with Sol among the Augustan poets of the first century, not even in the conjurations of Aeneas and Latinus in Aeneid XII (161-215). Apollo and Helios/Sol remained separate beings in literary and mythological texts until the third century CE.

Etymology

The etymology of Apollo is uncertain. Several instances of popular etymology are attested from ancient authors. Thus, Plato in Cratylus connects the name with "redeem", with "purification", and with "simple", in particular in reference to the Thessalian form of the name, , and finally with "ever-shooting". Hesychius connects the name Apollo with the Doric απελλα, which means "assembly", so that Apollo would be the god of political life, and he also gives the explanation σηκος ("fold"), in which case Apollo would be the god of flocks and herds. It is also possible that apellai derives from an old form of Apollo which can be equated with Appaliunas, an Anatolian god whose name possibly means "father lion" or "father light". The Greeks later associated Apollo's name with the Greek verb απολλυμι (apollymi) meaning "to destroy".