Thrasyllus of Mendes (/θrəˈsɪləs/; Ancient Greek: Θράσυλλος Thrasyllos), also known as Thrasyllus of Alexandria[1] and by his Roman name Tiberius Claudius Thrasyllus[2] (fl. second half of the 1st century BC and first half of the 1st century – died 36,[3][4]), was a Greek Egyptian[5] grammarian and literary commentator. Thrasyllus was an astrologer and a personal friend of the Roman emperor Tiberius,[4] as mentioned in the Annals by Tacitus and The Twelve Caesars by Suetonius.