Theodorus of Gadara was a Greek rhetorician of the 1st century BC who founded a rhetorical school in Gadara (present-day Jordan), where he taught future Roman emperor Tiberius the art of rhetoric. It was written of Tiberius that:
...even in his boyhood, his cruel and cold nature did not lie hidden. Theodorus of Gadara was his teacher of rhetoric and, in all his wisdom, seems to have been the first to have understood Tiberius and to have capped him with a very pithy saying when he taunted Tiberius, calling him 'Mud kneaded with blood'... (Suetonius, Lives of the Twelve Caesars).
His other well-known pupil was Greek rhetorician Hermagoras of Temnos, who later taught oratory in Rome.
Theodorus was one of the two most famous rhetoric teachers of the time, the other being Apollodorus of Pergamon. Students of Apollodorus were commonly referred to as Apollodoreans, while students of Theodorus were known as Theodoreans.
An eminent rhetorician of the age of Augustus, was a native of Gadara. He settled at Rhodes, where Tiberius, afterwards emperor, during his retirement (B.C. 6- A.D. 2) to that island, was one of his hearers (Sueton. Tib. 57). He also taught at Rome. Theodorus was the founder of a school of rhetoricians called "Theodorei."