Itylus

In Greek mythology, Itylus was the daughter of Aedon and King Zethus of Thebes. Aedon accidentally killed her and was stricken with grief and guilt. In pity, the gods turned her into a nightingale, which cries with sadness every night. Alternatively, Aedon attempted to kill the son of her rival, Niobe, also her sister-in-law, and accidentally killed her own daughter instead and thus, the gods again changed her into a nightingale.