Several months ago when I began reading "Claudius" by Douglas Jackson, I didn't realize that it was actually the sequel to "Caligula". Finding "Claudius" well researched with vibrant characters and taut action, I resolved to read "Caligula" as well.
"Caligula" fleshed out the backstory for Rufus, the young animal trainer who eventually became the emperor's elephant handler. Rufus is the central character in "Caligula", just as he was in "Claudius" and we experience the reign of the emperor Caligula as reflected in the interactions he has with Rufus and with those Rufus holds dear including Fronto, a procuror of beasts for the Roman games who purchases Rufus from a kindly baker, a rebellious gladiator named Cupido who becomes Rufus' best friend, the gladiator's beautiful sister and a diminutive woman chosen by the emperor to be Rufus' wife.
In the opening prologue, Jackson portrays Caligula as an already psychologically disturbed child who tortures little animals as he seeks to learn the limits of physical brutality. To the best of my knowledge, this is not documented in any ancient sources but it is effective to prepare the reader for some of the scenes of brutality that will follow as the scope of Caligula's brutaliy only increases with the power he acquires as the successor to the dour emperor Tiberius.