As the Nazgul hunt for Frodo during The Lord of the Rings they cover themselves in cloaks with no visible so what do they really look like?The Nazgul are the perfect representation of Saurons corruption as these former men are reduced to nothing more than slaves with no humanity left within them. During their search for Frodo in The Lord of the Rings they wear long black cloaks and armored gloves and under their hoods they appear as nothing but dark voids. And so, the question is raised what do the Nazgul actually look like?
While its unknown who each of the nine men was in The Lord of the Rings its known that they accepted rings of power from Sauron and were tricked into his corruption. Over time their will was completely bound to the Dark Lord and their former selves became so lost that they eventually passed into becoming wraiths. When Frodo wears the One Ring upon Weathertop he catches a glimpse of what the Nazgul once were with their kingly forms appearing gaunt and decayed. A common misconception in The Lord of the Rings is that when Frodo wears the One Ring he simply turns invisible. While that is somewhat true he actually passes through into the Wraith world which is a whole other realm laid on top of Middle earth. This is why Frodos vision becomes ghostly and the Nazgul appear vastly different he has viewing the Wraith world inside of which Sauron and the Nazgul are trapped. And so the forms Frodo sees are technically their true selves but not how they appear in the physical world.
While they are bound to the Wraith world the Nazgul can still pass through into Middle earth. But their forms are far weaker and less physical than before. While The Lord of the Rings novels never mention them when their cloaks are off there are a couple of moments that hint at their true forms. During their approach on Weathertop they are described as vague shadowy shapes and So black were they that they seemed like black holes in the deep shade behind them. So while its possible they still have their cloaks on in these moments the descriptions suggest they are nothing more than shadowy black figures underneath.This look would make sense as their bodies are still bound to the Wraith world. However it does raise questions as to why they would wear cloaks at all as being nearly invisible seems like a huge advantage. But the best guess is because they were searching for the One Ring they needed to appear to locals to ask about Baggins and the Shire. And ironically their cloaked appearances were far less horrifying than what was underneath.