Suetonius, ( in full : Gaius Suetonius Tranquillus) (about 70–140 A.D.), a Roman historian. His chief work, Lives of the Caesars , is a collection of biographies of the 12 Roman rulers from Julius Caesar to Domitian. This work emphasizes the rulers' personal lives rather than politics and is characterized by lively anecdotes. It is an important source for Roman history in the first century A.D. Suetonius was private secretary to the Roman emperor Hadrian, and had access to official records, which he used as sources.