Welcome fellow Athasian.
Except for the MC2 entry, there was only this from the Planescape MC
http://mojobob.com/roleplay/monstrousmanual/
One story of the origin of the ruvoka tells of a mortal prime named Garat who traveled to the Elemental Plane of Fire and accidentally wandered into the palace of Calif Alibashal, a powerful efreeti lord. Rather than being angry, the calif was amused by the intruder, and decided to inflict upon the sod the irony that he so enjoyed.
“Little mortal, I have summoned you,” the calif lied. “Now you must grant me one wish.”
This announcement surprised and worried Garat, yet he was canny enough not to contradict the efreeti. “Wise and wondrous Calif,” the prime said, bowing low, “grant me the pleasure of hearing your request.”
The efreeti lord smiled a toothy grin as his jest took form. “Ah, little man, I wish you to bring me the head of Baashizar, my rival.”
“Your words are wise and your wish is just. With your leave, I shall make your desires reality.” With that, Garat departed from the palace, fully intending to give it the laugh and never return. But he suddenly became curious. The efreeti was obviously playing a joke, but what would he do if Garat actually fulfilled his wish? The mortal came from the prime-material world of Athas, after all; he knew he was a strong and capable warrior and a clever spellcaster. He decided that he’d try.
Garat traveled many days across the plane of Fire to the lair of the efreeti known as Baashizar, then found his way through the lord’s traps and guardians. Suprising the efreeti at his own dinner table, Garat leapt at Baashizar and a terrible battle ensued that lasted for many hours.
Days later, Garat appeared again at the palace of Calif Alibashal. He held the head of Baashizar aloft. “Great and powerful Calif, as you have spoken, so have I done. Your wish was my command!”
Alibashal was so surprised and impressed that he called the mortal before him. “You are far more capable and loyal than I had dreamed, little man. Unlike the geniekind who are summoned to your worlds and forced to grant the wishes of others, you have done so willingly and efficiently. That is something worthy of respect. For your deed, I grant you immortality and life forever here in my realm. Further, those like you who follow in your steps shall gain homes throughout all the elemental spheres. We shall welcome such as you as our own.”
Garat, then, became the first of the ruvoka. And from then on, supposedly, mighty druids from tile Prime (a great many from Athas) journeyed to the Inner Planes and adopted them as their homes.