In Greek mythology, Cadmus (; Greek: Κάδμος, translit. Kádmos) was the legendary Phoenician founder of Boeotian Thebes. He was, alongside Perseus and Bellerophon, the greatest hero and slayer of monsters before the days of Heracles. Commonly stated to be a prince of Phoenicia, the son of king Agenor and queen Telephassa of Tyre, the brother of Phoenix, Cilix and Europa, Cadmus could trace his origins back to Zeus. Originally, he was sent by his royal parents to seek out and escort his sister Europa back to Tyre after she was abducted from the shores of Phoenicia by Zeus. In early accounts, Cadmus and Europa were instead the children of Phoenix. Cadmus founded or refounded the Greek city of Thebes, the acropolis of which was originally named Cadmeia in his honour.

Cadmus' homeland was the subject of significant disagreement among ancient authors. Apollodorus identifies it as Phoenicia, but Tyre, Sidon, and even Thebes in Egypt are referenced in different accounts. His parentage is sometimes modified to suit, e.g. claims of Theban origin name his mother as one of the daughters of Nilus, one of the Potamoi and deity of the Nile river.