A Gyrinx resembles a large cat, with very thick and fluffy ginger or orange fur and bright blue eyes. They can grow up to a meter in length. Gyrinx are not intelligent as such, but they have an astounding ability to empathize with other creatures, forming a mental bond with their owner which is comparable to true friendship. This mental empathy is of great benefit to the creature's owner, whose own speed of thought and action are actually improved while the Gyrinx is in close proximity. What benefit the Gyrinx obtains from the relationship is unclear, but there is plainly some deep-seated need being fulfilled, because an owner-less Gyrinx will actively seek out and adopt another creature. Oddly enough, Gyrinx show a slow metabolic change so that they can come to resemble their owner physically, temperamentally and in habit. If a Gyrinx's owner dies, it will defend the body, and will then either run away or allow itself to be adopted by one of its former owner's friends or associates. It takes a period of several weeks to establish a complete relationship with the new owner, but might be less if the old and new owners were close friends or relations.
Obviously, Gyrinxes are creatures of great value, and unlikely to be owned by ordinary people. Gyrinx are highly prized as pets by psychic Inquisitors, Rogue Traders and high-level members of the Ecclesiarchy and the like. Evil aliens, such as Dark Eldar, might also own Gyrinx -- the creatures inherit their owner's morality, which in turn, makes them become as nasty and vicious as their owners. Harlequin Shadowseers have also been known to take on a Gyrinx as a companion.
- Rogue Trader: Lure of the Expanse, (RPG), pg. 127
- Warhammer 40,000: Rogue Trader (1st Edition), pg. 213