Cadmus, in Greek legend, son of Agenor, king of Phoenicia and brother of Europa. After his sister had been carried off by Zeus, he was sent out to find her. Unsuccessful in his search, he came in the course of his wanderings to Delphi, where he consulted the oracle. He was ordered to give up his quest and follow a cow which would meet him, and to build a town on the spot where she should lie down exhausted. The cow met him in Phocis, and guided him to Boeotia, where he founded the city of Thebes. Intending to sacrifice the cow, he sent some of his companions to a neighbouring spring for water. They were slain by a dragon, which was in turn destroyed by Cadmus; and by the instructions of Athena he sowed its teeth in the ground, from which there sprang a race of fierce armed men, called Sparti (sown). By throwing a stone among them Cadmus caused them to fall upon each other till only five survived, who assisted him to build the Cadmeia or citadel of Thebes and became the founders of the noblest families of that city (Ovid, Metam. iii. 1 ff.; Apollodorus iii. 4, 5). Cadmus, however, because of this bloodshed, had to do penance for eight years.
At the expiration of this period the gods gave him to wife Harmonia (q.v.), daughter of Ares and Aphrodite, by whom he had a son Polydorus, and four daughters, Ino, Autonoë, Agave and Semele - a family which was overtaken by grievous misfortunes. At the marriage all the gods were present; Harmonia received as bridal gifts a peplos worked by Athena and a necklace made by Hephaestus. Cadmus is said to have finally retired with Harmonia to Illyria, where he became king. After death, he and his wife were changed into snakes, which watched the tomb while their souls were translated to the Elysian fields.
There is little doubt that Cadmus was originally a Boeotian, that is, a Greek hero. In later times the story of a Phoenician immigrant of that name became current, to whom was ascribed the introduction of the alphabet, the invention of agriculture and working in bronze and of civilization generally. But the name itself is Greek rather than Phoenician; and the fact that Hermes was worshipped in Samothrace under the name of Cadmus or Cadmilus seems to show that the Theban Cadmus was originally an ancestral Theban hero corresponding to the Samothracian. The name may mean "order," and be used to characterize one who introduces order and civilization.
The exhaustive article by O. Crusius in W.H. Roscher's Lexikon der Mythologie contains a list of modern authorities on the subject of Cadmus; see also O. Gruppe, De Cadmi Fabula (1891).