In Greek mythology, King Polydectes /ˌpɒlɪˈdɛktiːz/ (Greek: Πολυδέκτης) was the ruler of the island of Seriphos.
Polydectes was the son of either Magnes and an unnamed Naiad, or of Peristhenes and Androthoe, or of Poseidon and Cerebia. His story is largely a part of the myth of Perseus, and runs as follows according to the Bibliotheca and John Tzetzes. He was the brother of the fisherman Dictys who succeeded him on the throne.
Polydectes fell in love with Danaë when she and her son Perseus were saved by his brother Dictys (see: Acrisius). Perseus, old enough by the time, was very protective of his mother and wouldn't allow Polydectes near her. Therefore, Polydectes hatched a plot to get him out of the way. Under the pretence that he was going to marry Hippodamia, he ordered every man in Seriphos to supply him with suitable gifts. His friends were to provide horses but Perseus failed to bring any, so Polydectes announced that he wanted nothing more than the head of the Gorgon Medusa, being that Perseus had previously said he was up to a task so harsh as fetching a Gorgon's head. Perseus agreed and Polydectes told him that he could not return to the island without it. Perseus slew Medusa, supposedly using his shield as a mirror to avoid looking at her.