In Greek mythology, four people were known as Cycnus or Cygnus. Most of them ended up being transformed into swans.
- Son of Sthenelus and a good friend or lover of Phaeton. After Phaeton died, he dove repeatedly into the river Eridanos attempting to retrieve Phaeton's body. The gods turned him into a swan to relieve him of his pity.
- Son of Poseidon and a King of Colonae (in Troas). His second wife tricked him into trying to kill his son, Tenes. Tenes survived and both later supported the Trojans in the Trojan War. Achilles killed Cycnus and he was changed into a swan. (Ovid XII, 64)
- Son of Ares. He was a giant that was killed by Heracles.
- Son of Apollo, Cycnus was handsome but cruel and mean. Soon, he had only one friend that finally got fed up with Cycnus and killed him. Apollo turned him into a swan.
