Garth is Andrei Strasser's henchmen. In the film's opening, he and Strasser ambush a gorilla herd but baby Joe bites Strasser's fingers off forcing the two hunters to retreat.
Later Strasser and Garth see Joe on TV and both recognize him as the ape who bit Strasser's finger off. Strasser decides to go to America to get revenge on the ape for his severed hand.
Later, during a gala, Garth uses a poacher's noisemaker to scare Joe into a frenzy. Joe trashes the gala, recognizes Strasser and tries to attack him. Joe is then tranquilized and placed in a concrete bunker. When Jill learns that Joe may be euthanized, she decides to take Strasser's offer. Strasser uses the truck to get Joe inside with Jill's help.
Meanwhile, the refuge director Gregg O'Hara has realized that Strasser is a poacher (upon seeing the poaching noisemaker the maintenance had found) and goes after both Jill and Joe. On the way to the airport, Jill finally realizes who Strasser really is and ill punches Strasser in the face, hits him again and then kicks Garth in the head, before leaping out the truck and into the street. Joe Joe sees her and rocks the truck over onto its side and escapes. Strasser and Garth then hijack a man's car t search for the girl and the gorilla.Strasser arrives at the carnival and aims his gun at Jill. But Garth pushes Strasser's gun away from Jill, causing him to fire at a spotlight, which starts a fire and causes the Ferris wheel to break down. Realizing Strasser's true nature as a murderer, Garth tells Strasser that he quits, but Strasser knocks him out unconscious with his gun before leaving to confront Jill. It is unknown what happened to Garth afterwards.