Polydectes is Dictys's brother, and the king of the island where Perseus and Danae were washed up.
Polydectes, in contrast to Dictys, was cruel and ruthless, and one day he fell in love with Danae. He wanted to marry her, but first he decided that he must eliminate Perseus. He devised a plan where he proclaimed that he not like anything more than to have Medusa's head. Medusa's head turned anyone who stared into its eyes into stone. Later, Polydectes announced his wedding, and everyone gave him gifts except Perseus. In order to appease Polydectes, Perseus set out for the head.
Eventually, Danae and Dictys were forced to flee and hide from Polydectes, who grew wrathful for Danae's refusal to marrying him. When Perseus returned with Medusa's head, he displayed it in a banquet in Polydectes's palace, where Polydectes and his guests were instantly turned into stone, with the same expressions they bore the moment Perseus entered.