The Knights of Hell are a unique breed of demons that were created by Lucifer in order to be the strongest fighting force in the Inferno. They were said to have been created using a mixture of alchemy and ancient dark magic before being imbued with Lucifer's flames.
They are one of the oldest and most powerful demons in Hell, so much so that they are revered and praised by many demons for their prowess. They are also known for being rather defiant and refuse to obey demons they consider inferior to themselves, showing that they "inherited" Lucifer's rebellious nature during their creation.
When the Knights were created, they were commissioned by various lords of Hell in order to take on missions that are considered disastrous or "suicidal" for other demons to take part in. However, each Knight of Hell is not equal to the other, some vary depending on the training they go through and experience. They are powerful enough to be considered a great threat to even the angels, as few are even able to make a Seraphim, one of the more powerful celestial beings, struggle in battle against them.
Knights of Hell are said to possess powers that are rare or even unheard of among the legions of the damned, and even demonstrate fewer weakness than most other demons do. Example being that blessed objects can barely affect them, but it depends on the potency of the object while holy white light from angels can do little but singe them, however, archangels are able to completely destroy them. They are also regarded as one of the greatest fighters in the Demon World, to where they even have been known to train other demons in combat.
However, after the rebellion from a certain Knight, the Knights of Hell became officially defunct and vanished. Some were even hunted and killed by demon lords in fear that they too will rebel against them and assume command over the various of regions and kingdoms in Hell. It is rumored that very few Knights are living among the humans and following a peaceful lifestyle.