Princes of Chaos

CHAOTIC PAST: Demons of the planes are evil creatures and chaotic by natures. Demon's themselves existed in the planes in the age of the chaotic dark long before light and the existence of the gods. The earliest of demons were known as obyriths  The demons would find their place in the layers of the Abyss.
Through the ages, demons fought among themselves for power to rule over the Abyss and eventually all of the realm. In addition to fighting  each other, a Blood War was waged with their greatest enemies, the devils of the nine hells. In comparison of demons to devils, devils follow a hierarchy of devils while demons have no such structure in place, but each to have their own interpretation of power. 
The unstructured nature of demons makes them both a powerful and unpredictable enemy, but also holds them back from destroying the realm. Each demon in one way or another wants to see themselves as the most powerful creature to rule the realm. However, they each do have a sense of their own power and others goals. To attack another demon would weaken their own strength making them a prime target for an attack. Instead of grand marching of demonic armies, they tend to make small scale expansions of their territories in the Abyss, yet constantly plotting for a greater goal.
BAPHOMET: A demon prince who rules over the endless maze in the abyss. He resembles a minotaur and is also known as the horned king. He divides the realm into two categories, his servants who acknowledge his strength and prey. He loves the hunt of his prey. His amusement is never greater than to watch hopeless enter his victims as he has outsmarted and overpowered them.
Worshippers: Those who worship Baphomet are predisposed to believing they are superior to other living beings to the extent others are just feral animals. Worshipping Baphomet may allow him to favor his followers with keen skills of savagery and cunning. A follower may be a sociopathic noble who sees his serfs as play things or an assassin which finds pleasure in their work.
DEMOGORGON: Demogorgon is consider the prince of Deomon's. His mangled figure is that of webbed feet, tentacle arms, and ape like body and two ape like heads. The two heads are of separate mind cooperating in some ways and opposing in others. Demogorgon is in a state of constant paranoia to hold his title in the chaos of the Abyss. His ultimate goal is to destroy all living things so he may finally be at peace.
Worshippers: Majority of Demogorgon's followers are lesser demons as he commands unmatched followers. Some demons may be corrupted by his mere presence and become enslaved to him. Some mortals may become corrupted by looking into a true symbol of Demogorgon. Those mortals now corrupted act as an agent to kill unsuspecting victims leaving only terror behind when the bodies are discovered.
GRAZ'ZT: Graz'zt was once an archdevil who served Asmodeus. Sent into the Abyss to destroy demons, he became corrupted. He turned away from the devils and ruled over his conquered territories. He finds himself to be the Lord of pleasure and limitless indulgence. He sets forth to destroy anything which does not offer him pleasure.
Worshippers: His followers are those who seek self pleasure above all others. Graz'zt offers promises for dark delights and forbidden pleasures in exchange for submission to him. 
ORCUS: The Prince of the Undead. He hates the living. He finds the living as nothing but noisy, crude, and maddening. Life is seen as nothing but a hamster wheel with a squeaking fulcrum. Mortals and gods claim to achieve great things, but never truly accomplish anything. Orcus does not love anything including his followers. If a devout worshipper killed 1,000 souls, Orcus would be disappointed in how long the effort took. 
His motives are unclear. It is hard to develop a sense for something as evil and seemingly chaotic as Orcus. Some believe that he wants to destroy all of the universe until he is the last living thing. Others believe he wants to replace the noise of life with the hum of stagnant undeath, at which point he would find peace. 
During the war tales spread of Orcus playing both sides. Stories of undead armies rising to finish off the short lived victories after a long fought battle spread across the armies of the lands. It is rumored an attempt to summon the demon prince had taken place, but efforts were vanquished by a band of heros who managed to separate Orcus from his wand and through it deep into the underdark below the capital city of Malatrick. 
Worshippers: Cultists of Orcus are heretics and blasphemers seeing the gods as unjust and cruel. They resent that mortals must suffer and die at the whims of the gods. Someone who has lost a loved in a tragic event. In Orcus they see true freedom and release from pain without demand of obedience. In a state of undeath there is no hunger, pain, or suffering.  
A devout worshipper would become corrupted and be turned undead. Often, the transformation would give them unnatural powers as a necromancer, vampire, or lich.