The Apocolocyntosis by Seneca the Younger.
When the Emperor Claudius died in 54 A.D., Suetonius describes in The Twelve Caesars how Nero spoke at his funeral: "Then beginning with a display of filial piety, he gave Claudius a magnificent funeral, spoke his eulogy, and deified him." This eulogy had been written by Seneca the Younger, and elsewhere, such as in De Consolatione ad Polybium, there is evidence of Seneca praising Claudius. In 55 A.D. however Seneca had rather changed his tune.
The Apocolocyntosis, which comes from the Greek word Ἀποκολοκύντωσις meaning 'gourdification' or 'pumpkinification', is also known as The Gourdification of the Divine Claudius and it's a dramatisation of the death of Claudius, his ascent to heaven, judgement, and subsequent descent to Hades. It begins,
The purpose of the following work is to give future generations an account of the events in heaven on the thirteenth of October of this strange year of grace that inaugurated our present period of prosperity. No offence and no flattery is intended. What follows is the honest truth. If the reader asks for my sources, in the first place I will refuse to answer if I am not so inclined. Who is going to make me? I know that I'm a free man ever since the death of the fellow who proved the old saying - be born a king or a fool! Should I wish to answer, I'll say the first thing that comes to my lips. Whoever demanded a sworn witness from an historian? But it is necessary to reveal my source, you should ask the man who saw Drusilla's ascent into heaven. This person claims he saw Claudius making the same journey, though 'with shorter steps'. Willy-nilly, he has to watch everything that does on in heaven - he's in charge of Appian Way, the way by which, as you know, the Divine Augustus and Tiberius Caesar joined the company of the gods. If you ask him, he'll tell you in private. He'll never say a word more than one. Ever since he swore in the senate that he'd seen Drusilla going up to heave and, for all that marvellous news, no one believed him, he has solemnly sworn that he will never reveal what he's seen, even if it's a murder in the middle of the Forum. I am here setting down clearly and precisely the unimpeachable story he have me and of course I trust he is well and flourishing.
From here Seneca describes how Mercury asked Clotho to end Claudius' life, and how Claudius walks to Mount Olympus to ask Heracles to hear his reasons for deification. This goes well until it is time for Augustus to speak, and he gives a damning account of Claudius' numerous short-comings. His application is then denied and he is escorted down to Hades, on the way witnessing his own funeral procession. Once in Hades he is greeted by all those he murdered.
Despite sounding rather grim, it's actually very funny in the typically Roman way (fart jokes are, of course, present: Romans seemed to like a fart joke). It's very untypical of Seneca, though, however whilst there's not universal consensus he actually did write it, many believe he did. There appears to be a few motivations for it: Seneca's anger at being exiled by Claudius, wanting to get in with the new Emperor Nero, and annoyance at the deification of previous emperors, making him fear that this would lead to people losing their faith in the gods. Whatever the case, it's a fantastic read!