Guy Mann is the pseudonym of a lizard creature.
He was bitten by a human and transforms into one semi-randomly. It was as a human that he first recognised his self-consiousness, and developed a number of human motivations, ranging from revenge, to job hunting and worrying about his retirement.
Hating his transformation, he saw a "witch doctor" and believed that he needed to be killed by being stabbed by a piece of sharp green glass into his appendix.
Guy is initially the main suspect of a murder inquiry, leading Fox Mulder and Dana Scully to question him. Fleeing from Scully he escapes to a nearby cemetary where he encounters Mulder, and explains his story.
Ultimately the murderer is discovered to be Pasha, the local Animal containment officer. After he has been arrested Mulder rushes to the forest to break the news to Guy, who tells him that he is about to hibernate for 10,000 years, hoping that he can sleep off his transformations. He transforms back into his natural lizard form whilst shaking hands with Mulder, before running off into the night. (TXF : "Mulder and Scully Meet the Were-Monster")