Tereus was a king of Thrace in Greek mythology, son of the god of war Ares. He was married to Procne, with whom he had a son, Itys.
Tereus lusted for Procne's sister, Philomela, and one night, he raped her. After the rape, he cut off her tongue, so that she would not be able to tell anyone the truth, and he held her captive; he then told Procne that her sister had died. However, Philomela managed to weave what had happened onto a tapestry and sent it to Procne. When Procne read her sister's story, she killed her son Itys, and fed him to Tereus. Upon finding out about Procne's crime, Tereus tried to kill both sisters, but before he was able to, the gods changed all three into birds; Tereus was transformed into a hoopoe; Procne, mourning for her child's death, turned into a nightingale; while Philomela turned into a swallow.
See Also: Ares, Procne, Philomela