When the Dark Lord came upon this earth much evil soon followed. Demons and Devils soon found their way to this world. The Shadow Demons were the first to come forth. Six men who so faithfully followed the Dark Lord that they gave their soles to him. They became the Shadow Demons, evil wraith like creatures that defiled the land.
Demons
Demons are native to the infernal planes of the Abyss. They are the most violent, greedy, fickle, and perverse of the creatures from the lower planes. Demons come in an overwhelming variety of forms. Most are unique but there are some that can be catagorized. They agressivly seek to make this world their own.
Devils
Devils are fiends who are infamous for their strength, evil temperment and ruthlessly efficient organization. Devils are less likely to reside on this plane than Demons, prefering to extend their influence by corupting mortals. Devils are lawful evil and have a rigid caste system. Devils are more easily catagorised than demons but still each is an individual and many are unique.
Since the Dark Lord's riseing demons and devils have found their way onto this plane.
This is done by one of two ways.
Assention
Is how the Dark Lord came to this world. This is the ritual of a mortal traiding his life and sole for the fiend. When the fiend assends the mortal may keep some consiousness but more than likely simply ceases to exist. The fiend uses the mortals body but molds it to his form. This is the easyest way for fiends to come to this plane but a mortal must be willing to sacrafice his sole. This is how the Dark Lord and the shadow demons came to this plane.
Transention
is the opening of a 'gate' from the Abyss to this world. There are many ways a gate can be opened. In some places there are perpetual gates, called Hell Gates. Other gates may be temporarily opened through ritual, powerful magic, or other means. Here the physical form of the fiend crosses planes. This is the hardest way for a fiend to cross. Even finding a perpetual gate dose not garuntee transention.