Cadmus, in Greek mythology, Phoenician prince who founded the city of Thebes in Greece. When his sister Europa was kidnapped by the god Zeus, Cadmus was ordered by his father, the king of Phoenicia, to find her or not to return home. Unable to locate his sister, he consulted the oracle at Delphi and was instructed to abandon his search and instead to found a city. Upon leaving Delphi, the oracle advised, Cadmus would come upon a heifer, follow her, and build the city where she lay down to rest.

Near the site of the new city Cadmus and his companions found a sacred grove guarded by a dragon. After the beast killed his companions, Cadmus slew the dragon and, on the advice of the goddess Athena, planted its teeth in the ground. Armed men sprang from the teeth and fought each other until all but five were killed. Cadmus enlisted the help of the victors in founding the citadel of the new city of Thebes, and they became the heads of its noble families. Before Cadmus could enjoy his new home, however, he had to do penance for killing the dragon, which was sacred to Ares, god of war. After eight years of servitude, Cadmus was made king of Thebes and was given Harmonia, the daughter of Ares and of Aphrodite, the goddess of love, as his wife.

Although Thebes prospered under Cadmus's rule, misfortune overcame his descendants. In his old age, after two of his daughters and two of his grandsons had suffered violent deaths, Cadmus fled with his wife to Illyria, where at his death he and Harmonia were changed into serpents. According to tradition, Cadmus introduced the alphabet into Greece.