MacGruder is the right-hand man of the film's main antagonist, Michael Jennings. Though he carries out Jennings's dirty deeds to the best of his abilities (which are sometimes disastrously inadequate), he isn't loyal enough to risk his life for him.
MacGruder is a simpering minion who is only brave and confident when facing much weaker opponents or surrounded by armed thugs. Though he presents himself as a dangerous man, he is in fact an easily rattled coward.
MacGruder's first major villainous act is invading the home of Forrest Taft's friend, Hugh Palmer, while looking for a floppy disk containing incriminating data. When Hugh refuses to cooperate, MacGruder breaks his fingers and tortures him with a pipe-cutter. Forrest is then led into an explosive trap, where he finds Hugh's body shortly before MacGruder detonates it. Despite the massive explosion, Forrest survives—Jenning knows this in his gut and orders MacGruder to search for him, which leads the henchman to the Eskimo tribe that nursed Forrest back to health. Forrest's coat is found, and MacGruder demands the tribe to tell him where Forrest is; in what he claims to be self-defense, he kills the tribe's chief Silook.
MacGruder later accompanies Stone and his mercenary force on the hunt for Forrest; with the use of several explosive traps, Forrest escapes, and MacGruder realizes that Forrest is going to Jennings' main rig.
After causing critical damage to the Aegis 1 rig, Forrest finds MacGruder about to take off in a helicopter and shoots the tail rotor to stop it from lifting off. Forrest grabs MacGruder before he can run away and, after a brief struggle, MacGruder is shoved into the helicopter's tail rotor killing him and avenging Hugh and Silook.