Gaius Suetonius Tranquillus is mainly remembered as the author of De Vita Caesarum [commonly known as The Twelve Caesars, is a set of twelve biographies of Julius Caesar and the first 11 emperors of the Roman Empire],his only extant work except for the brief biographies. The Twelve Caesars, probably written in Hadrian's time, is a collective biography of the Roman Empire's first leaders, Julius Caesar (the first few chapters are missing), Augustus, Tiberius, Caligula, Claudius, Nero, Galba, Otho, Vitellius, Vespasian, Titus and Domitian. The book was dedicated to his friend Gaius Septicius Clarus, a prefect of the Praetorian Guard in 119.