Demons (D&D)

Demons are a hostile race of Fiends from the Dungeons & Dragons fantasy role-playing multiverse - they are normally designed for high-level adventurers but come in many different forms and levels, the most powerful of the Demons are known as Demon Lords and are virtually deity-level threats (in contrast some of the weakest Demons are capable of being defeated by mid-to-low tier mortal adventurers).

History
Demons are a recurring high-level antagonistic force in Dungeons & Dragons, being the Chaotic Evil opposite of the Lawful Evil Devils - whom they are at near-constant war with and thus both utilize mortal souls as a means to try and win the war, it is believed by many sources that if either Devils or Demons won the war the end of all realms would begin as the victor would finally have the power to flood all other realms with their particular branch of evil.

Demons are a type of Fiend (just like their hated enemy, the Devils) and reside in the Abyss - a realm that embodies chaotic evil, as such all inhabitants of said realm are also included towards chaotic evil behavior and ideals.

This makes Demons naturally prone to extreme violence, cruelty and malice - they delight in war, the suffering of others bring them equal joy and they desire nothing short of the destruction of all things, valuing nothing save brutal strength, which is the only means to truly control them.. even then they will quickly find ways to betray or murder those that try and command them unless they retain their strength : only the most violent, feared and murderous of Demons are thus capable of keeping lasting power within the chaotic hordes.

Demons seek out mortal souls so as to create more Demons, the more souls they can steal the more potential soldiers they can form to go into battle - they also know that this will rob the Devils of a similar supply, thus potentially bringing the Demons closer to victory in the Blood War.

The inclusion of Demons (alongside Devils) in early editions of Dragons & Dragons contributed to the false assumption by certain groups that the game was actually Satanic in nature - this panic caused Wizards of the Coast to lower the appearance / references to Demons and Devils for a short while but as of the modern edition they are back as one of the most prominent threats higher-level parties may encounter.