Gaius Suetonius Tranquillus (Latin: [ˈɡaːiʊs sweːˈtoːniʊs traŋˈkᶣɪlːʊs]), commonly known as Suetonius (/swɪˈoʊniəs/ SWIH-toh-NEE-əs; c. AD 69 – after AD 122), was a Roman historian. His most important work is called De Vita Caesarum, or Lives of the Caesars. It includes the biographies of twelve successive Roman rulers, from Julius Caesar to Domitian.