In Greek mythology, the name Chthonius or Chthonios (Greek: Χθόνιος "of the earth or underworld") may refer to: * Chthonius, one of the five surviving Spartoi in Thebes, father of Lycus and Nycteus (but see Hyrieus). * Chthonius, one of the sons of Aegyptus and Caliadne, who married and was killed by Bryce, daughter of Danaus and Polyxo. * Chthonius, son of Poseidon and Syme, who founded the first colony on the island of Syme, which was named after his mother. * Chthonius, a Centaur who was killed by Nestor at the wedding of Pirithous and Hippodamia. * Chthonius, one of the Gigantes. * Chthonius, an epithet of several major gods, including Zeus, Hades, Hermes, and Dionysus. See Chthonia for goddesses bearing the feminine version of the epithet.