In Greek mythology, Semele, daughter of Cadmus and Harmonia, was the mortal mother of Dionysus by Zeus in one of his many origin myths. (In another version of his mythic origin, he had two mothers, Persephone and Semele.) The name "Semele", like other elements of Dionysiac cult (e.g., thyrsus and dithyramb), is manifestly not Greek but apparently Thraco-Phrygian; the myth of Semele's father Cadmus gives him a Phoenician origin. Herodotus, who gives the account of Cadmus, estimates that Semele lived sixteen hundred years before his time, or around 2000 B.C.
In one version of the myth, Semele was a priestess of Zeus, and on one occasion was observed by Zeus as she slaughtered a bull at his altar and afterwards swam in the river Asopus to cleanse herself of the blood. Flying over the scene in the guise of an eagle, Zeus fell in love with Semele and afterwards repeatedly visited her secretly.
Zeus' wife, Hera, a goddess jealous of usurpers, discovered his affair with Semele when she later became pregnant. Appearing as an old crone, Hera befriended Semele, who confided in her that her lover was actually Zeus. Hera pretended not to believe her, and planted seeds of doubt in Semele's mind. Curious, Semele demanded of Zeus that he reveal himself in all his glory as proof of his godhood. Though Zeus begged her not to ask this, she persisted and he agreed. Mortals, however, cannot look upon Zeus without dying, and she perished, consumed in lightning-ignited flame.
Zeus rescued the fetal Dionysos, however, by sewing him into his thigh (whence the epithet Eiraphiotes, "insewn", of the Homeric Hymn). A few months later, Dionysus was born. This leads to his being called "the twice-born".
When he grew up, Dionysos rescued his mother from Hades, and she became a goddess on Mount Olympus, with the new name Thyone, presiding over the frenzy inspired by her son Dionysos.
In another version of the same story, Dionysus, the son of Zeus and Persephone, the queen of the underworld, is called Zagreus, and was dismembered by the Titans, at the instigation of Hera. Gaius Julius Hyginus, or a later author whose work has been attributed to Hyginus, said Zeus created mead out of Zagreus's heart, which he gave to Semele to drink, and that this was how she became pregnant.
Dionysus, who was called "the twice-born" because of being sewn, when still a foetus, into his father's thigh (see above), "was also called Dimetor [of two mothers] ... because the two Dionysoi were born of one father, but of two mothers" According to Ellie Crystal, the rebirth in both versions of the story is the primary reason he was worshipped in mystery religions, as his death and rebirth were events of mystical reverence, and this narrative was apparently used in certain Greek and Roman mystery religions. Variants of the narrative are found in Callimachus and the Fifth Century CE Greek writer Nonnus. In the passage in question Nonnus does not present the conception as virginal; rather, the editor's notes imply Zeus swallowed Zagreus' heart, and visited the mortal woman Semele, whom he seduced and made pregnant. In Dionysiaca 7.110 he classifies Zeus's affair with Semele as one in a set of twelve, the other eleven women on whom he begot children being Io, Europa, the nymph Pluto, Danaë, Aigina, Antiope, Leda, Dia, Alcmene, Laodameia, mother of Sarpedon, and Olympias.
Though the Greek myth of Semele was localized in Thebes, the fragmentary Homeric Hymn to Dionysus makes the place where Zeus gave a second birth to the god a distant one, and mythically vague:
Semele was worshipped at Athens at the Lenaia, when a yearling bull, emblematic of Dionysus, was sacrificed to her. One-ninth was burnt on the altar in the Hellenic way; the rest was torn and eaten raw by the votaries.
Semele was a tragedy by Aeschylus; it has been lost, save a few lines quoted by other writers, and a papyrus fragment from Oxyrhynchus, P. Oxy. 2164.