Tereus is a character from Greek mythology, known primarily for his tragic story involving betrayal and violence. He was a Thracian king who married Procne, the sister of Philomela. Tereus is infamous for committing a heinous act against Philomela, which led to a series of tragic events. In revenge for Tereus's actions, Procne and Philomela plotted against him. They killed Tereus and served him his own son in a gruesome meal. This act of vengeance transformed the three characters into birds: Tereus became a hoopoe, Procne a nightingale, and Philomela a swallow, symbolizing their tragic fates.