The publication of Robert Graves's I, Claudius in 1934 marked a distinct turning point in the development of English historical fiction. Most earlier works were either set in relatively recent and familiar time periods (Charles Dickens's A Tale of Two Cities and Barnaby Rudge, for example) or, if set in the more remote past (like Sir Walter Scott's Ivanhoe), present a romanticised view of that past, rooted in the concerns of the society that produced them.
Graves, on the other hand, took a remote time period and, on the basis of assiduous historical research, presented it to the reader in all its fascinating otherness. In doing so, he broke down the distinction between "serious" and "popular" writing, making available to a broad readership an awareness and a familiarity with a past that had previously been accessible only to scholars who had an intimacy with Latin and Greek. This prepared the way for several generations of writers of historical fiction, including Mary Renault, Rosemary Sutcliff and, in our own time, Colleen McCullough.
Crucial to his success in establishing and popularising a new genre of fiction was the scholarship that underpins Graves's historical writing (he draws extensively on the works of Suetonius, Tacitus, Cassius Dio, Flavius Josephus and other classical writers, often shining a light into corners of the past that they leave dark), as well as the characterisation of his protaganist. Marginalised by virtue of his real and perceived disabilities, Claudius is an outsider at the courts of Augustus, Tiberius and Caligula, able to record events from the perspective of an observer rather than a participant.
Humour is an essential part of this characterisation: Claudius is a dry, ironic observer, prone to gossip and to speculation, an unreliable observer in a way that is very human and, consequently, engaging. He is by no means a hero, but as a guide to the machinations and insanities of the court he is both informative and entertaining, constantly whispering asides to the reader.
He is probably a more genial character than the historical Claudius was (Suetonius describes Claudius as "cruel," "bloodthirsty," "cowardly and suspicious"), just as his grandmother, Livia, is portrayed by Graves as a far more villainous individual than she probably was in reality. But this is fiction, after all. That we have constantly to remind ourselves of this fact, to take care to disentangle Graves's Claudius from the historical one, is a testament to the power of Graves's writing: the sign of a masterpiece that is, in Hilary Mantel's words, "sympathetic and intensely involving: a great feat of imagination."