Robert Graves wrote the novel “I, Claudius”. It’s about the Roman emperor Claudius. It includes history up to the murder of Caligula, and starts sometime before Julius Caesar's reign. The various reigns covered include a couple of the most famous Roman emperors, such as Caesar. It is ranked 14th on the list of best novels from the 20th century. “Time” magazine even ranked it as one of the best novels written between 1923 and the present. It’s actually the first book in a duet of books about Claudius the Roman emperor.
The emperor was actually considered to be mentally ill because of a variety of physical malformities - a limp, a stutter, etc. He was coronated at the age of 49, after his entire family was killed. He wasn’t considered a threat.