In Greek mythology, Cycnus (Ancient Greek: Κύκνος "swan") Cygnus or Cidnus[1] was a king of Liguria, a beloved and lover of Phaethon, who lamented his death and was subsequently turned into a swan and then a constellation.

[9] Swans are known for mourning their mate for many days when they die, which suggests that Cygnus and Phaethon were lovers.

[13] Pausanias mentions Cycnus, king of the Ligyes (Ligurians), as a renowned musician who after his death was changed into a swan by Apollo.

[14] Servius also writes of Cycnus as a musician and a friend of Phaethon, and states that he was changed into a swan and later placed among the stars by Apollo (that is, as the constellation Cygnus).

[7] Cycnus' profession as a musician may be a direct reference to the concept of the swan song suggested in Hyginus' account.