A little while after I wrote my Arch-devil profile for Dicefreaks, I ended up writing another such profile, this time for a Demon Prince. I kinda like this one better -- it's an original character (albeit named after a Biblical figure), so I was able to be a little more creative instead of sticking to D&D continuity.
Originally Rahab was named Dagon (and was largely inspired by the Lovecraft-derived B-movie of the same name), but I had to change it because the project already had a devil named Dagon. Oddly enough, a few years later, an official D&D sourcebook came out with a version of Dagon practically identical to the one I wrote below. (See here for Rahab w/full game stats done up by a fellow poster.)
RAHAB (Vepar, Sorath, Dagon)
The Demon Prince of the Lightless Depths, the Deep One, the Lord of the Deeps, Mariner's Bane, the Bringer of Storms
Symbol: A single round eye with no iris or pupil.
One of the most dreadful of the horrors of the Abyss, Rahab, the Demon Prince of the Lightless Depths, is a tentacled monstrosity that desires nothing less than the domination of all seas. One of the oldest demons in existance, the primordial horror that is Rahab is a creature of slime, darkness, and insanity that only the strongest of wills can stand to look upon without losing their mind.
Rahab's realm is the 873rd layer of the Abyss: the Lightless Depths. A water-filled realm, the Depths are literally without light: anyone without darkvision can see absolutely nothing in this layer. Here, Rahab swims through the black abyss, devouring the souls of those foolish or insane enough to call him their master. Unlike most other Demon Princes, Rahab shares his realm with several other powerful beings, including a number of myrmyxicuses. At one time he fought for his layer with dread King of the Deep, a demonic entity once beholden to the will of the now-dead goddess Takhisis, but the King was slain by heroes on the world of Krynn, and now Rahab's dominion over the Depths is unquestioned. It is likely that various other unique demons call the Depths home as well. These lesser horrors generally leave Rahab alone, and flee before his might when he approaches.
Like many fiends, Rahab is known by many names. Some of his followers speak of him as Vepar and others as Sorath. Some cultists know him as Dagon, but that name rightfully belongs to one of Hell's devils.
Because their "portfolios" overlap in regards to the slimy dwellers of the deep, Rahab is a sworn enemy of both the Demiurge Demogorgon and the dread Hadean god Panzuriel, but because of Rahab's relative weakness, clashes between their forces tend to be rare. Among the other powers he has made an enemy of are Sekolah of the sahuagin; Blibdoolpoolp of the kuo-toa; Eadro of the merfolk and locathah; Deep Sashelas of the elves; the Elemental Prince Ben-Hadar; and the human gods Aegir, Umberlee, and Poseidon. Of these, Poseidon is by far his deadliest rival: the Sea Father has sworn an oath to rid his oceans of Rahab's evil influence. It is common for Poseidon to recruit powerful heroes to brave the Lightless Depths and spy on his cultists' doings in the hopes that some headway might be made in his war against the demon. The Duke of Hell known as Dagon loathes Rahab as well for allowing the demon's followers to know him as Dagon.
Unsurprisingly, Rahab has virtually no friends. The only ally he has is Olhydra, the Princess of Evil Water. Because of the distance between their realms, however, and Olhydra's fickle nature, he has not found her a very reliable ally.
The goals of Rahab are the destruction of good sea life (such as aquatic elves) and the domination of neutral and evil denizens of the oceans. He has many worshippers among the creatures of slime and muck that dwell on the seabed: koprus, anguiliians, kuo-toas, ixitxachitls, rogue sahuagin, and even some renegade merfolk pay Rahab homage. All of these races have their own unique, foul rites that they perform in Rahab's name.
Rahab has a fairly widespread following of human cultists on the Prime Material Plane. Many a coastal fishing town has found itself at the mercy of a poor harvest and turned to Rahab-worship in hopes of rectifying the situation. Indeed, Rahab frequently rewards his worshippers with greater catches of fish and harvests of grain, as well as gifts of gold. Such cultists make a common practice of summoning their demonic master to their plane of existance and offering a living sacrifice - indeed, Rahab actually encourages his followers to summon him. Such conjurations give him an opportunity to spread his corruption, transforming his worshippers into maddened inhuman reflections of their old selves, creatures of slime as hideous as their master. Such summonings typically involve a blood sacrifice and the destruction of a small golden pyramid inscribed on each face with his unholy symbol.
Rahab is truly hideous. Only vaguely humanoid in shape, the Demon Prince of the Lightless Depths is a gargantuan cephalopoid monster. He looks something like a bloated, rubbery octopus, with a head like a human skull, a single cyclopean eye with no pupil set in its center. In place of a mouth, Rahab has a mass of ten-foot-long tentacles that dangle writhing from his head. Rahab has two huge tentacle-arms like those of an octopus that branch at each of their midpoints into ten squirming appendages. From his 'waist' depend twenty or more tentacles. His overall color is a dark green-brown, but Rahab can change his color to suit his whim. In addition to this hideous form, he can also change at will into a handsome merman some twenty feet from head to tail, with dark green skin and green-brown scales; he adopts this shape when summoned to the Prime by his human followers.