Traveller's rat is a unique member of the collective of rats that watches over the world of T.O.E. He has been tasked with accompanying Traveller, and goes to great pains to keep Traveller far away from the borders of the Imperium. The rat masquerades as a voice in Traveller's head to remain incognito, and hides in Traveller's hair or clothing to escape detection.
Traveller's rat is somewhat duplicitous: not only does it hide its true nature from Traveller, it plays tricks with Traveller's poor memory to keep him disoriented. Because the rat has been away from its kin for so long, however, it appears to have forgotten the purpose for keeping Traveller within the Imperium, remembering only that the reason is very important. It also has trouble sorting out the lies it has told Traveller from the truth.
Traveller's rat is perhaps the most expressive of its kind. Though appropriately mystical in its speech most of the time, it has shown regret for tricking Traveller in his journeys. It is also prone to bouts of fear, rage and irritation, and even gave Iko the finger.
After being found by Iko in the desert, Traveller's rat was outed by the hermit. It has been locked in a small cage and offered as a pet to Traveller on his journey to find Dragomir.
The rat has been named Vimhtaar by the fans. Traveller probably doesn't have the brain power to come up with such a sobriquet on his own.