Titus Livius (64? BCE-9 CE) is sometimes referred to as the "national historian of Rome." His Ab Urbe Condita (History of Rome), however, was not an officially-sanctioned account, but rather a life-work; its 142 books were a thing begun on his own initiative while he was still youngish, and which he worked on for almost the rest of his time on earth.
We don't have the books dealing with the late Republic and the reign of Augustus, so we can't be sure how he treated events in those times. But other historians mention them, saying Livy held off publishing the most recent parts until after Augustus' death: raising the possibility that the Princeps just might have found them offensive had he been permitted to see them. Livy himself never sought public office, so he was beholden to neither the power structure nor the populace. He could write what he liked.
The writing of history back then was not the same as the researched-and-documented attempt at objectivity that it is nowadays. Livy's purpose, most of all, was to tell a moral History of Rome, by presenting a series of character-studies.
We know these people: Horatius, Camillus, Cincinnatus, Scaevola... all those stories that are still told as examples of Roman courage and rectitude. We read about the worship of a certain God falling into decline, and are not surprised when the next campaign season finds Roma suffering military reverses. Acts of propitiation are performed, and things get better again. A Consul who has lost almost Rome's entire military-age population in a single battle returns home in seeming disgrace--and is commended by the Senate for "not having despaired of the Republic". Livy is full of stories like this. This makes him one of the most accessible Roman historians, and for many a favorite.
Livy's History gave early-Imperial Rome a common ground. By spelling out the Heritage, he made unity possible. Not always probable...but possible. Everyone knew the heroes, the tales, the lessons to be drawn from them. Poets dropped the heroes' names with no further explanation required. Satirists hinted with a sly grin that they knew what the hero was really up to. But they were all talking about the same thing, about stories a young Roman would have heard on his tutor's or his pater's knee.
One way Titus Livius is of immense value to us is that he shows us what was important to the Romans, and how they preferred to think of themselves. Like any self-concept, this one contains inaccuracies. But like any other, even having it available gives us a priceless insight into the Roman mind, one that has the power to change our own self-concepts, just a little.
This is the thing we are trying to live up to...which alone is a token of Livy's success.