Gaius Julius Caesar (13 July 100 - 15 March 44 BCE), Roman statesman, general, author, famous for the conquest of Gaul (modern France and Belgium) and his subsequent coup d'état. He changed the Roman republic into a monarchy and laid the foundations of a truly Mediterranean empire.
Most entertaining is the biography by Gaius Suetonius Tranquillus, which is the first of the Lives of the twelve Caesars. The biographer was in charge of the imperial archives under the emperor Hadrian (who ruled 117-138): in this capacity, Suetonius had access to some of the best possible information. He uses it critically: for example, about Caesar's death circulated a story that he had expected the assault, but was shocked to discover that Brutus was one of the conspirators, and that his last words were '"You too, my son?" Suetonius makes clear that he has some doubts about this anecdote.
Describing someone's life is a meaningless thing to do, unless there is some moral to be learned. Suetonius' moral is clear: if a man has the total freedom and the absolute power of a Roman emperor, he must be strong indeed if he wants to remain honest. To show this, he is fond of stories about cruelty and sexual deviations. Of course, this makes him one of the most interesting authors of antiquity, but sometimes he seems to portray his emperors a nuance too black.
Another moralist is the Greek author Plutarch of Chaeronea (45-120 CE), who was a few years younger than Suetonius and covered more or less the same ground. His biography is meant as a counterpart to a Life of Alexander the Great: consequently, the moral is totally different, namely that Greeks and Romans have much more in common than they want to admit.
These two biographies give us the outline of Caesar's life, a mere skeleton. It should be given flesh with other information, for which Caesar's own writings are very important.
The correspondence of Cicero cannot be dismissed. To a large extent, his Letters to Atticus are private correspondence and they give us first-rate information about the political life in Rome in Caesar's days. As these letters were rediscovered during the reign of Caesar's descendant Nero (who was emperor 54-68 CE), several unbecoming letters about Caesar were not published. The same selection was made in the collections of Cicero's Letters to Friends and Letters to Brutus. Cicero's speeches are very informative, especially On the provinces for the consuls, For Marcellus, For Ligarius and the Philippic speeches against Mark Antony.
On Caesar's behavior in 63, our most important source is The Catiline Conspiracy by Caesar's partisan Sallust, or -to use his full name- Gaius Sallustius Crispus (86-34 BCE). Perhaps he is also the author of a Letter to Caesar, in which the author suggests some reforms.
The books on Caesar by the historian Titus Livius (59 BCE - 17 CE; better known as Livy) have not survived, but excerpts are still extant. It is possible that Plutarch used this text when he wrote his biographies: his Life of Caesar has already been mentioned, but biographies of Brutus, Cato the Younger, Cicero, Crassus, Mark Antony and Pompey are most informative too. In the first quarter of the third century, the Greek historian Cassius Dio based part of his description of the fall of the Roman Republic (books 36-44 of his Roman History) on Livy. For the struggle over Caesar's inheritance, he is undoubtedly our most important source.
There's an awful lot of modern literature on the subject, although most of it deals with details. A good start is the Cambridge Ancient History, volume IX of the second edition (1994), "The last age of the Roman Republic", edited by J.A. Crook, A. Lintott and E. Rawson.