All we know about Caesar in Gaul is that he was a decisive, clever, and daring commander who persevered against overwhelming odds.
How do we know all this is true? Do we have other evidence other than Caesar’s self-aggrandising memoirs in the Comentarii de Bello Gallico?
It looks like later imperial historians also had vested interest in painting a flattering picture of Caesar - as the legitimacy of the emperors relied on Caesar’s name.
So, what is the actual evidence of Caesar’s exploits in Gaul - other than his own testimony? Could it be that he - with a numerically and technologically superior army - just steamrolled isolated pockets of local resistance? How do we know that an average late Republican general couldn’t have done the same?
Cicero delivered a speech about Caesar's campaign, the de provinciis consularibus, and mentions the campaign in several letters, including a few to his brother Quintus, who was one of Caesar's legates and is mentioned in the BG sever times. Sallust was a contemporary of Caesar, as was Hirtius. We know that Livy wrote about Caesar and have a general understanding of the contents of those books from the Periochae. Pollio, though lost, was used extensively by later authors as a source.
It looks like later imperial historians also had vested interest in painting a flattering picture of Caesar - as the legitimacy of the emperors relied on Caesar’s name
Quite the contrary. Plutarch, Appian, Suetonius, and Cassius Dio, our primary post-Caesarian sources, are quite critical of Caesar and present, at best, an ambiguous picture of him. That the emperors traced their legitimacy to Caesar is essentially irrelevant. Emperors were faced all the time with predecessors whose reigns and lives were distasteful to them, and had no compunctions whatsoever with denigrating the memories of previous rulers. Moreover, the emperors did not write our surviving histories. With the possible exception of Cassius Dio none of our surviving histories that discuss Caesar can be reasonably said to be "official" in any sense of the word. Most are quite the opposite. Livy, we know, treated Caesar as a tyrannical figure. Pollio's reception of Caesar was similarly mixed, and we know that Pollio's ambiguous appraisal of Caesar is echoed (in a few cases directly quoted) in the historians who used him, especially Suetonius and Plutarch. Tacitus openly lamented the loss of liberty under Caesar, even if he argued that autocracy is a teleological inevitability for any free society. All three were authors who were openly critical of the imperial regime. Plutarch was a foreigner, and has little interest in the Principate. Caesar is explicitly the villain, or at best the antihero, of Lucan's Pharsalia. Writers do not necessarily hold the same opinions as the political structures under which they live