Gaius Suetonius Tranquillus, commonly known as Suetonius (c. 69 - after 122 AD), was a Roman historian belonging to the equestrian order who wrote during the early Imperial era of the Roman Empire.His most important surviving work is a set of biographies of twelve successive Roman rulers, from Julius Caesar to Domitian, entitled De Vita Caesarum, or The Lives Of The Twelve Caesars.