Fenrus (aka Fenris and Feyhnrus) is the rat Familiar of the Wizard Erasmus and a Wizard himself. He is a known member of RABID (Rodents Against Boring Idiosyncratic Discrimination). Being the Familiar to such a powerful wizard, Fenrus himself possesses formidable magical prowess (he often jokes that Erasmus is really his Familiar). He appears as a large rat with hands instead of paws and wears a blue magical cap.
Fenrus always accompanies Erasmus, and like the whimsical wizard, he appears in four out of the five Quest for Glory games.
He earned his Wizard status, and Master of Arcane Arts from Mythcatonic U. He was Erasmus' familiar even before he learned magic.
In So You Want to Be a Hero, he is present at Erasmus's Zauberberg Mountain and provides some useful bits of information for the Hero. Through magical communication with Erasmus, Fenrus can also be heard joking in Quest for Glory II: Trial by Fire when the player is a magic-using character, after the magic user enters the Wizard's Institute of Technocery (W.I.T.) and request Erasmus as his sponsor. Both Fenrus and Erasmus also make cameos in the fourth game, Shadows of Darkness, being heard occasionally while the Hero sleeps and more importantly at the end (to summon him from Mordavia to Silmaria and set up the fifth game).
Finally, Fenrus again appeared in Quest for Glory V: Dragon Fire. Erasmus functions here much the same as he did in the first game, although at a point fairly early in the game Erasmus is drugged, falling into a deep sleep. Fenrus first summons the apothecary Salim Nafs and his healer wife Julanar, but they are unable to wake the Wizard. Thankfully, Fenrus has enough magical power to keep Erasmus's floating castle from falling out of the sky. The Hero is able to heal Erasmus by giving him the waters of Lethe (although he does not wake up until the very end of the game). If Katrina or Erana do not summon allies to the final battle against the Dragon, Fenrus will appear and summon them instead.