About the book (from Wikipedia):
De vita Caesarum (About the Life of the Caesars) commonly known as The Twelve Caesars, is a set of twelve biographies of Julius Caesar and the first 11 emperors of the Roman Empire written by Gaius Suetonius Tranquillus.
The work, written in AD 121 during the reign of the emperor Hadrian, was the most popular work of Suetonius, at that time Hadrian’s personal secretary, and is the largest among his surviving writings. It was dedicated to a friend, the Praetorian prefect Gaius Septicius Clarus.
The Twelve Caesars is considered very significant in antiquity and remains a primary source on Roman history. The book discusses the significant and critical period of the Principate from the end of the Republic to the reign of Domitian; comparisons are often made with Tacitus whose surviving works document a similar period.
About Suetonius (from Wikipedia):
Gaius Suetonius Tranquillus, commonly known as Suetonius (c. 69 – after 122 AD), was a Roman historian belonging to the equestrian order who wrote during the early Imperial era of the Roman Empire.
His most important surviving work is a set of biographies of twelve successive Roman rulers, from Julius Caesar to Domitian, entitled De Vita Caesarum. He recorded the earliest accounts of Julius Caesar’s epileptic seizures. Other works by Suetonius concern the daily life of Rome, politics, oratory, and the lives of famous writers, including poets, historians, and grammarians. A few of these books have partially survived, but many have been lost.