Theagenes (Greek: Θεαγένης; fl. c. 160 AD) of Patras, was a Cynic philosopher and close friend of Peregrinus Proteus. He is known principally as a character who appears in Lucian's The Death of Peregrinus (Latin: De Morte Peregrini), where he is introduced as praising Peregrinus' desire to kill himself by self-immolation: Theagenes is also mentioned by Galen, who recalls how he lectured daily to large crowds in Trajan's Forum in Rome. Galen describes how Theagenes died when he was given an inappropriate treatment by (physician to Marcus Aurelius) for inflammation of the liver.