Vrumugun is the name given to a group of copy men created by Eris, who serve as antagonists during the first season of Slayers and the third novel.

In the novels, Eris used the Vrumuguns to try and capture Lina Inverse, Gourry Gabriev, and Zelgadis Greywords and bring them to Sairaag. However, she only sent one Vrumugun after them at a time, sending a new copy every time one was killed. This greatly confused Lina and co. at first, because no matter how many times they killed Vrumugun, he kept re-appearing (they had thought that Vrumugun was a single person, not a group of copies). The Vrumugun copies disappeared once their controller died. In the anime, he was grouped with Zangulus as they tried to capture Gourry and Lina. However, while Zangulus was short-tempered and arrogant, Vrumugun was quiet, collected, and took everything seriously. Strangely in episode 18, after Zelgadis kills a group of clones, Vrumugun vanishes and is never seen again for the remainder of season 1.
There is much ambiguity as to who the original Vrumugun is, since they never say specifically in any of the Slayers mediums. In the novels, there is evidence to suggest that Eris is the original. She (and possibly the original Rezo) created them, and her last name is also Vrumugun. In the anime, on the other hand, Eris' last name is never mentioned, nor is it ever hinted that she is the original. Furthermore, at the end of Slayers NEXT, we see, albeit only briefly, a person very much resembling Vrumugun at Zangulus and Martina's wedding. It is implied that this person is the original Vrumugun.

(Source: Wikipedia)