1. A son of Apollo by Thyria or Hyria, the daughter of Amphinomus. He was a handsome hunter, living in the district between Pleuron and Calydon, and although beloved by many, repulsed all his lovers, and only one, Phyllius, persevered in his love. Cycnus at last imposed upon him three labours, viz. to kill a lion without weapons, to catch alive some monstrous vultures which devoured men, and with his own hand to lead a bull to the altar of Zeus. Phyllius accomplished these tasks, but as, in accordance with a request of Heracles, he refused giving to Phyllius a bull which he had received as a prize, Cycnus was exasperated at the refusal, and leaped into lake Canope, which was henceforth called after him the Cycnean lake. His mother Thyria followed him, and both were metamorphosed by Apollo into swans. (Antonin. Lib. 12.) Ovid (Met. vii. 371, &c.), who relates the same story, makes the Cycnean lake arise from Hyria melting away in tears at the death of her son.
2. A son of Poseidon by Calyce (Calycia), Harpale, or Scamandrodice. (Hygin. Fab. 157; Schol. ad Pind. Ol. ii. 147; Tzetz. ad Lycoph. 233.) He was born in secret, and was exposed on the sea-coast, where he was found by shepherds, who seeing a swan descending upon him, called him Cycnus. When he had grown up to manhood, he became king of Colonae in Troas, and married Procleia, the daughter of Laomedon or of Clytius (Paus. x. 14. § 2), by whom he became the father of Tenes and Hemithea. Dictys Cretensis (ii. 13) mentions different children. After the death of Procleia, he married Philonome, a daughter of Craugasus, who fell in love with Tenes, her stepson, and not being listened to by him calumniated him, so that Cycnus in his anger threw his son together with Hemithea in a chest into the sea. According to others Cycnus himself leaped into the sea. (Virg. Aen. ii. 21.) Afterwards, when Cycnus learned the truth respecting his wife's conduct, he killed Philonome and went to his son, who had landed in the island of Tenedos, and had become king there. According to some traditions, Tenes did not allow his father to land, but cut off the anchor. (Conon, Narrat. 28; Paus. x. 14. § 2.) In the war of the Greeks against Troy, both Cycnus and Tenes assisted the Trojans, but both were slain by Achilles. As Cycnus could not be wounded by iron, Achilles strangled him with the thong of his helmet, or by striking him with a stone. (Comp. Diod. v. 83; Strab. xiii. p. 604; Schol. ad Theocrit. xvi. 49; Dict. Cret. ii. 12, &c.; Ov. Met. xii. 144.) Ovid adds, that the body of Cycnus disappeared and was changed into a swan, when Achilles came to take away his armour.
3. A son of Ares and Pelopia, challenged Heracles to single combat at Itone, and was killed in the contest. (Apollod. ii. 7. § 7; Hesiod. Scut. Herc. 345, where Cycnus is a son-in-law of Ceyx, to whom Heracles is going.)
4. A son of Ares and Pyrene, was likewise killed by Heracles in single combat. (Apollod. ii. 5. § 11; Schol. ad Pind. Ol. xi. 19.) At his death he was changed by his father Ares into a swan. (Eustath. ad Hom. p. 254.) The last two personages are often confounded with each other, on account of the resemblance existing between the stories about them. (Schol. ad Pind. Ol. ii. 147, ad Aristoph. Ran. 963; Hygin. Fab. 31; Athen. ix. p. 393.)
5. A son of Sthenelus, king of the Ligurians, and a friend and relation of Phaëton. He was the father of Cinyras and Cupauo. While he was lamenting the fate of Phaëton on the banks of the Eridanus, he was metamorphosed by Apollo into a swan, and placed among the stars. (Ov. Meet. ii. 366, &c.; Paus. i. 30. § 3; Serv. ad Aen. x. 189.)
6. A sixth personage of the name of Cycnus is mentioned by Hyginus. (Fab. 97.)