As we all know, Darth Sidious/Emperor Palpatine appeared throughout The Empire Strikes Back and The Return of the Jedi sporting his signature hooded cloak.
And a handsome devil he was too.
I'm unclear why exactly he wore a cloak during this time period, though. During the prequels it's understandable that the personas of Palpatine and Sidious needed to be distinctly separated. His plan for the Clone Wars and taking over the Senate necessarily required subterfuge. If Palpatine had been discovered to be working with the Separatists and the likes of Maul then it would have left his schemes in ruin. Using a cloak to disguise his appearance therefore makes sense when sending transmissions to the likes of Nute Gunray.
But when he had consolidated his power by becoming Emperor surely the need for secrecy was unnecessary. Any attempt to keep his Sith persona under-wraps and remain a simple politician (albeit an emperor) was because it suited his purposes politically to do so. However, if that was his intent then suddenly changing from wearing the garments of a Chancellor of the Republic to a creepy hooded robe associated with the Sith and the Jedi seems bizarre. Wouldn't his new clothing lead to unwelcome questions if all he wanted was an uncomplicated transfer from Chancellor Palpatine to Emperor Palpatine in the eyes of the public?
I haven't been able to find much other than joke answers online so far. I can think of a few possible explanations but don't have anything to back them up.
To hide his identity
Maybe he really didn't want people to see his face or to know who he was. This doesn't really make any sense given that he was already famous galaxy-wide for being the Chancellor. Everyone knows who he is anyway.
Because that's what Sith wear
Out-of-universe, this makes sense. The robes make him look evil and intimidating. However, this answer and this answer demonstrate to my satisfaction that he didn't want his Sith powers to be public knowledge.
Because he's Emperor so he can do what he wants
This is the point made in the Reddit thread. Given that he starts wearing his hood straight after taking office and is still sticking with it 20 years later I can't help thinking there must be a more substantial reason than this.
Because he was self-conscious
It's true that his encounter with Windu left him with some serious facial injuries. He says himself in his speech to the Senate that "the attempt on my life has left me scarred and deformed", and uses this to generate sympathy and to cast himself as the victim of Jedi aggression. I'm wondering if there's any evidence that he also felt embarrassed and humiliated by his appearance? Could he really have just worn the cloak because he was insecure?