Gaius Suetonius Tranquillus was a Roman historian and biographer who lived during the 1st and 2nd centuries AD. He is best known for his work "The Twelve Caesars," a set of biographies of Julius Caesar and the first 11 emperors of the Roman Empire. Suetonius' writings provide valuable insights into the lives and reigns of these influential figures, and his work has had a lasting impact on the study of Roman history.