Short answers, pulled from the story.
The Twelve Caesars was written by Gaius Suetonius Tranquillus in 121 AD. Suetonius was serving as personal secretary to the emperor Hadrian at the time and dedicated the work to his friend Gaius Septicius Clarus, the Praetorian prefect.
The Twelve Caesars covers Julius Caesar and the first eleven emperors of the Roman Principate: Augustus, Tiberius, Caligula, Claudius, Nero, Galba, Otho, Vitellius, Vespasian, Titus, and Domitian.
The Twelve Caesars is one of the enduring primary sources for classical scholarship, alongside the works of Tacitus. For certain emperors, including Caligula, Claudius, and Vespasian, Suetonius is the major surviving source because other accounts, such as the relevant sections of Tacitus' Annals, have been lost.
Historians criticize The Twelve Caesars as racy and sensationalist, overly reliant on gossip, and prone to sacrificing accuracy for drama or humor. Suetonius lost access to the official archives partway through his work and was forced to rely on secondhand accounts, and he omits several important events for unknown reasons.
The oldest surviving copy was made in Tours in the late 8th or early 9th century AD and is currently held in the Bibliothèque nationale de France. It is missing the prologue and the opening section of the life of Julius Caesar, as are all other surviving copies. There are nineteen surviving copies from the 13th century or earlier.
Marius Maximus modeled his biographies of later emperors on The Twelve Caesars, and in the 9th century Einhard borrowed phrases from Suetonius' description of Augustus when writing his Life of Charlemagne. Robert Graves published a widely read translation through Penguin Classics in 1957, and Titian created a series of paintings based on the twelve Caesars.