He was voiced by Peter MacNicol who originally played Dr. Janosz Poha in Ghostbusters II.
Not a lot is known about him, but he is very timid, cowardly, apprehensive, and easily intimidated. He is also prone to panic when his boss is upset. Quiet, peaceful, soft-spoken, imperturbable, and middle-witted, he is averagely competent and consummate, so he can come up with good ideas at times, but he is a complaisant and docile wimp. He is also very heartbreaking and pitiful, but can still be called a villain.
Role in the film
When the Anti-Recess Group took over a military testing site to steal the weather altering laser that was in development in the area, he managed to shut down the alarms, before telling Benedict that the situation is now all clear, before learning that their next move is to covertly take over Third Street School when summer begins. Later on, Fenwick was tasked with finding the principal's office, although he doesn't see what's so significant about it that would necessitate Benedict to find it for him, before Benedict reveals that the reason it's significant for him is because he used to work there before Peter Prickly replaced him. He is later told off along with the other personnel in regards to the failures regarding the laser (referring to the earlier forced terminated test of the weather altering laser that was unintentionally revealed to TJ and his gang). After it became apparent that TJ and the others snuck into the school (Mikey was unable to hold in a belch developing inside him, and the vents they were observing in gave way), Fenwick was briefly questioned by Benedict as to who let kids in the school before Benedict screamed for his men to get them, resulting in TJ's capture. Later on, after Gretchen managed to black out the lab that used to be the auditorium, Fenwick and some scientists was tasked to fix the fuse (under the belief that it was the result of a blown fuse), although they ended up locked inside of the power room by Gretchen. Having somehow managed to get out and supply a backup generator, they then attempt to proceed with the laser as planned, even with a fight between Benedict's forces and a joint group of students and teachers. At the end, Benedict and his men (including Fenwick) end up being arrested for their crimes; as Fenwick is being escorted to a police car, he cried out that he was just following Benedict's orders and offers to give in state's evidence for the trial, but the arresting officer refuses and puts in him the car. Even the local school snitch Randal Weems was appalled at the offer, saying "Jeez, what a squealer!".