Honorius
Theodosius's son, Honorius was as much of a religious persecutor, but with an additional xenophobic slant. He seems to have hated anyone of Germanic descent, even his best general, Stilicho, who was half-Vandal half-Roman, but born and raised in the empire as a Roman. His top general,
Stilicho, who had successfully negotiated a peace with Persia and defeated all barbarian invasions during his long career, never losing a single battle, was imprisoned by Honorius and executed in 408 without a fair trial. This was followed by a pogrom against all and any Germanic people living in Italy, including the thousands serving in the Roman army, which Honorius couldn't stand. This left the Western Empire virtually defenceless, allowing the Suebi, Vandals, Alans and Burgundians to carve their own kingdoms within the borders of the empire, then Alaric to sack Rome in 410 and the abandonement of Britain by the Romans the same year. Honorius's bigotry, racism, narrow-mindedness and incompetence hastened the fall of the Western Roman Empire. In fact, there was hardly anything left of the Western Empire outside of Italy after his reign.
https://www.eupedia.com/history/best_and_worst_roman_emperors.shtml
The worst of the worst is someone who never gets the glamour of Caligula or Nero. To be fair to Caligula and Nero, they actually did stuff. There is nothing glamorous about Honorius, a man who formed his own personal power vacuum at a time when the Western Empire – structurally weakened via division from the East – sorely needed an active leader. Honorius, like US President James Buchanan in 1857, inherited an awkward situation, and turned it into a catastrophe through mind-numbing incompetence.
This was a period where Rome was under intense pressure from barbarians. The one guy who was left frantically holding the situation together? A general named Stilicho, who ran around saving the day again and again (sure, he made mistakes too, but they were understandable mistakes, and at least he was trying). Honorius – under urging from one of his ministers – had Stilicho executed. Not just that, but he purged (and tortured!) all Stilicho’s associates too. That’s what competence gets you under Honorius.
As for the barbarians, the Gothic leader Alaric had made deals with Stilicho. The Goths wanted some land, and, all things considered, what Alaric was offering was a pretty decent deal for the Empire. With the death of Stilicho, Honorius told Alaric to get stuffed. Then his new adviser turned around and mass-murdered thousands of Gothic women and children. Alaric forced the city of Rome to make extensive concessions. Honorius then screwed Alaric over again.
Alaric sacked Rome in A.D. 410, to make an understandable point. It wasn’t even a nasty sack (that would wait for A.D. 455), and it wasn’t even the first time in living memory Rome had suffered for screwing over barbarians (*cough* Adrianople in 378 *cough*)… but it was a massive loss of prestige. One entirely avoidable, and one that can be laid fairly at the feet of Honorius.
The sixth century Byzantine Historian, Procopius, provides an anecdote about Honorius’ response to the Sack:
“At that time they say that the Emperor Honorius in Ravenna received the message from one of the eunuchs, evidently a keeper of the poultry, that Rome had perished. And he cried out and said, ‘And yet it has just eaten from my hands!’ For he had a very large cock, Rome by name; and the eunuch comprehending his words said that it was the city of Rome which had perished at the hands of Alaric, and the emperor with a sigh of relief answered quickly: ‘But I thought that my fowl Rome had perished.’ So great, they say, was the folly with which this emperor was possessed.”
Procopius was writing more than a century afterwards, so take the anecdote with a grain of salt, but one gets the picture of how the Emperor was viewed in late Antiquity. It’s not a flattering portrait.
(Also, in contrast to the accusations against Caligula, this is less about a tyrant oppressing the elite, and more about a muppet who let the Empire fall. I know which one triggers my Badness Detector more).
The cherry on top is that Honorius was also the Emperor who told the British to look after themselves, as far as defence was concerned. Yes, Rome was in no position to defend its British citizens, given that it had other concerns, but those other concerns were a reflection of Honorius’ mismanagement.
I am not a fan of Great Man History (or in this case Terrible Man History), and it would be wrong to pin the collapse of the Western Empire on Honorius. There are always deeper causes for things like this, and I do take the view that the bigger mystery is how the Western Empire lasted as long as it did, given the structural and economic headwinds. But to see Honorius’ regrettably lengthy reign as anything other than twenty-eight years of disaster and mismanagement, at the worst possible time, is simply impossible. Honorius gets my vote as the Worst Emperor Rome ever had.