There is little known on Caligula's reign since so few sources have survived, but he was described as a noble and fair ruler during the first two years of his rule. After those years though, well that’s when it got bad. Sources focus purely on his cruelty, sexual perversity and lavishness. He was presented as a psychotic tyrant, leading many people to believe that he had neurosyphylis.
These ancient sources may not be the most reliable though, but what is known is that during his short reign Caligula worked to increase the power of the princeps, something that didn’t make folks too happy. He also focused a lot of his attention to over-the-top construction projects, like new fancy homes for himself, but also two new aqueducts for the city of Rome (Aqua Claudia and Anio Novus). But, these two primarily associated with his successor Claudius, who was the one that brought these projects to completion.
On January 24, 41 A.D. Caligula was assassinated as the result of a conspiracy involving the members of the Roman Senate, officers of the Praetorian Guard and of the imperial court.
Now that we’ve got the history out of the way you may be wondering what the hell all of this has to do with vampires. Well, after his death the rumor was that Caligula returned as one of the undead, haunting Lamia Gardens and the Esquiline Hill on which he was buried. He was taken there after his murder, given a hasty half cremation and placed in a shallow grave. Eventually the rumors supposedly caused them to go back to exhume him and give him a proper cremation. But even after this was done, they couldn’t stop the stories that Caligula walked the gardens and the hill, therefore they acquired an evil reputation.