In F. Paul Wilson's novels, the rakoshi (singular: rakosh) are demon-like creatures from ancient India.
Roughly humanoid, the rakosh stand about eight feet tall, with cobalt blue skin and malevolent yellow eyes. They are incredibly strong, fast, and agile, and are armed with viscious fangs and razor-sharp claws on each of their three-fingered hands.
Rakoshi are virtually immune to almost all forms of attack, and feel no pain whatsoever. Iron can weaken them, but only fire can destroy them.
According to legend, ancient Old Ones, who predateded the Vedic and pre-Vedic gods, sought to take over mankind's place on earth. To this end, they took some humans and stripped them of everything good and decent, making them "hate, lust, greed, and violence incarnate." Giving the rakoshi an insatiable appetitie for human flesh, the Old Ones set them forth on earth to take humanity's place.
Fortunately, humans turned out to be smarter than the creatures, and learned to control them. Ancient priests finally imprisoned the last of the rakoshi in caves in northern Bengal, and built a temple to Kali above. For generations, they kept and controlled the rakoshi. The Keepers of the Rakoshi wore magical necklaces, forged from iron and set with a pair of yellow stones resembling the creatures eyes, which healed them, prolonged their lives, and rendered them invisible to the rakoshi.