Gaius Suetonius Tranquillus is better known simply as  Suetonius, and is famous for his biography usually called The Twelve Caesars. This was one of the first examples of a history told in as a chronology of leaders. Along with the works of Tacitus, Suetonius is the primary source of historical biographical data for the period of the early Empire.
Suetonius was a prominent Roman born into an equestrian family in 69 in Hippo Regius, in what is modern day Algeria. His father Suetonius Laetus, was a colonal in the army and served with the Emperor Otho at the Battle of Bedriacum for the Emperor Otho in 69.
Suetonius became a close friend and ally of the politician and historian Pliny the Younger. Through his friendship to Pliny, Suetonius obtained property in Italy and was introduced to the inner circle of the Emperor Trajan.
When Pliny was elected Proconsul of the province of Bithynia Pontus in 110, Suetonius joined his is staff and traveled to Asia Minor to serve with his friend. When the proconsulship ended in 112, Suetonius returned to Rome and became Secretary of Studies and Director of The Imperial Archives under Trajan. Later he became the personal secretary of the Emperor Hadrian.
However in 122, Hadrian dismissed him for disrespectful behaviour towards Empress Vibia Sabina.  Suetonius became a writer and began work on his history of the Emperors starting with Julius Caesar and ending with Domitian. He went onto write a number of books including books on Grammar and language, biographies of poets including Virgil, and rhetoricians, a commentary on Cicero’s Republic, a biography of famous prostitutes and a life of Pliny The Elder. Most of these works have been lost. There is some evidence he made his way back into Hadrian’s good books as his last work was called Offices of State and dealt with Hadrian’s legislative reforms.

The Twelve Caesars

De Vita Caesarum or "Lives of the Caesars" is better known in English as "The Twelve Caesars.”  The Twelve Caesars, was probably written during Hadrian's reign and is the only work by Suetonius that remains in almost its entirety. The first few chapters of the Julius Caesar biography have been lost. The work is a collective biography of the Roman Empire's first 12 leaders starting with Julius Caesar then describing the lives of Augustus, Tiberius, Caligula, Claudius, Nero, Galba, Otho, Vitellius, Vespasian, Titus and, finally, Domitian.
The Lives follows the same formula and describes each life in the same way by detailing the Emperor’s appearance, omens, family history, quotes, and then a chronological history. While he tries to avoid moralizing, Suetonius does criticize those emperors who amassed wealth at the expense of the Roman middle class.
Suetonius used his access to official sources, private documents, gossip, witnesses, histories and primary sources as well as personal observation to craft biographies unparalleled at the time. His work became the basis for the later work of Robert Graves’ famous ‘I, Claudius’ and influenced generations of Roman biographers and historians.
While modern historians will find infuriating Suetonius’ fleeting references to certain characters and events that would warrant further explanation, his wit and ability to joke about his subjects sets him apart from many dry classical writers.