Apollodorus reckons Magnes among the seven sons born to Aeolus, king about Thessaly, and Enarete, daughter of Deimachus — set in the catalogue beside Cretheus, Sisyphus, Athamas, Salmoneus, Deion and Perieres. He is a minor figure of the founding generation, remembered less for his own deeds than for the line he begot.2Pseudo-Apollodorus — Bibliotheca 1.7.3

Magnes married a Naiad nymph, and to him were born two sons, Polydectes and Dictys; these colonized Seriphos. With that single sentence the genealogist plants the Aeolid stock on the island where Danae's chest would one day come ashore.3Pseudo-Apollodorus — Bibliotheca 1.9.6

Through his sons Magnes' house locks into the Perseus cycle. Apollodorus makes Polydectes king of Seriphos and the villain of the tale: in love with Danae but barred by the grown Perseus, he feigns to collect a wedding gift and so dispatches the youth for the Gorgon's head — while Dictys and Danae take refuge at the altars, and Perseus, returning, turns the tyrant and his friends to stone with Medusa's face and appoints Dictys king. Ovid likewise paints Polydectes as the rancorous king of 'Little Seriphos' who calls the hero's deeds a fraud, and is made bloodless stone for it.4Pseudo-Apollodorus · Ovid — Bibliotheca 2.4.2–2.4.3; Metamorphoses 5.279–398

Hyginus tells the brothers' part more gently. The fisherman Dictys finds the floating chest and breaks it open, discovering mother and child; he brings them to King Polydectes, who weds Danae and rears Perseus in the temple of Minerva, and even intercedes for them when Acrisius comes seeking their lives — Perseus swearing never to kill his grandfather. Here Polydectes is no petrified tyrant: he dies of his own, and only at his funeral games does Perseus' discus, blown astray, strike Acrisius dead. So the same two sons of Magnes stand as rescuers in this telling, and the king as protector rather than foe.5Hyginus — Fabulae 63