The Kuluu are an ancient race that existed 10,000 years before present day Final Fantasy XI.
10,000 years ago Vana'diel was a playground to the Zilart race. During this time, a growing number of Zilart were found to be lacking "The Whisper of the Soul"—an ability allowing the Zilart to communicate telepathically—due to the formation of Emptiness inside of them. Seen as abominations, the ones lacking "The Whisper" were cast out the Zilart's capital city, Al'Taieu. Left to fend for themselves in the wilderness, these outcasts eventually became known as the Kuluu.
The Kuluu endured the harsh environments in the wilds of Vana'diel, discovering ways to survive and the magic of Summoning Avatars. Eventually the Kuluu rose to build cities of their own, centered around the magical Avatars. Worried of their growing power, the Zilart conquered the cities and subjugated the Kuluu, creating amulets to allow them to hear the whisper of the soul, as and The Chamber of Eventide to purge the Emptiness from the Kuluu.
The Kuluu saw near extinction along with the rest of Vana'diel's inhabitants after sabotaging the Zilartian plans to open the Gates of Paradise and become one with the Gods. An explosion resulting from the sabotage damaged the very core of Vana'diel, but ultimately saved the planet. Those who survived the blast retreated into the city ruins, and over the next 10,000 years damaged energy from the blast slowly warped the remaining Kuluu from their once peaceful race into the cold-hearted Tonberry Beastmen.
Remnants of Kuluu civilization can be seen across Vana'diel - namely, in every Tonberry. The Temple of Uggalepih is one example of a ruined Kuluu city.