Cadmus was the founder and first king of Thebes in Greek mythology. He was the son of King Agenor and Queen Telephassa of the Phoenician city of Tyre, and brother of Phoenix, Cilix and Europa. It was believed that he was the person who introduced the Phoenician alphabet to the Greeks, who then adapted it into their own.
Cadmus set out on returning his sister Europa back to Phoenicia after she was abducted by Zeus, commanded by his father. As he was unwilling to go against a god's will, he ended up in the island of Samothrace, accompanied by his mother and his nephew, Thasus; the latter gave his name to the nearby island of Thasos. Cadmus met the goddess Harmonia there, who would later become his wife.
The young prince later found himself consulting the oracle of Delphi, in order to continue the search for his sister. He was told to stop his search; instead, he should follow a cow that bore a half moon on her side, and build a city on the spot where the animal would rest. That was how Thebes was founded, the first building being a shrine to Selene, goddess of the moon.
Cadmus decided to sacrifice the cow to Athena, and asked his companions to bring water from a nearby spring. There, a water-dragon killed all of them, but Cadmus eventually managed to kill the beast. Following Athena's advice, he took the teeth of the dragon and placed them in the soil, out of which a legion of fierce men, the Spartoi, sprang out. Cadmus killed all but five of them, with whom he built the city.
The dragon, however, was protected by the god of war, Ares, who demanded that Cadmus serve him for eight years. After that period, Cadmus married Harmonia at the gods' request; in their wedding, Harmonia received a necklace from Hephaestus, the so-called Necklace of Harmonia, which brought ill fortune to anyone who possessed it. This brought maladies both to Cadmus' family and his city. Cadmus and Harmonia had a number of children; they were Ino, Polydorus, Autonoe, Agave, Semele and Illyrius.
In the end, Cadmus and Harmonia left Thebes and went to the region of Illyria. Cadmus, worn out by the ill fate that the gods had brought upon him for killing the dragon, wished that he transform into a serpent himself; his wish was granted and he started growing scales immediately. Harmonia then asked for the same fate as her husband, and it was also granted.