He is an experienced Scottish combat pilot, an RAF squadron leader, and a loyal comrade-in-arms to the protagonist, B.J. Blazkowicz. Fergus is known for his thick Scottish accent, rough humor, cynicism, and endless supply of sarcasm traits that mask a devoted friend and a war-weary soldier.

Relationship: B.J. Blazkowicz: Best friend, brother-in-arms, and object of genuine admiration. Attitude: Fergus is loyal to B.J. to the very end. He is the only person Blazkowicz truly heeds as a commander. Fergus sees him as an unstoppable force but also sincerely sympathizes with his grim fate. Communication style: He constantly teases B.J. about his melodramatic internal monologues and gloomy demeanor. He calls him "Big John" or simply "Lad." If Blazkowicz recklessly rushes into danger, Fergus will scream profanities at him but solely out of fear of losing a friend.

The scientist Set Roth creates a high-tech mechanical prosthetic for Fergus, powered by the advanced technology of the extinct Da'at Yichud order. However, something goes wrong: the prosthetic connects directly to Fergus's nervous system but develops a "mind" of its own. Fergus struggles immensely with his new arm due to two main issues: constant rebellion and obscene gestures. The arm frequently refuses to obey Fergus's commands. At the most inopportune moments, it takes on a life of its own clenching into a fist, scratching Fergus's backside, or spontaneously flipping the bird at those around him (including Blazkowicz and Grace). Fergus has to literally hold his right arm down with his left, cursing at it loud enough for the whole submarine to hear. Losing an arm after a drinking bout: There is a hilarious quest in the game. After a wild party celebrating Blazkowicz's birthday, Fergus wakes up dead drunk to find his arm has run off somewhere. It literally detached itself and crawled away. Blazkowicz has to scour the entire submarine to find the prosthetic. It turns out the arm managed to climb into the ventilation system, got stuck behind some boxes, and kept furiously wiggling its fingers.

Grace Walker. Status: New boss (leader of the American Resistance). Relationship: Very strained and tense. Fergus is a career RAF officer accustomed to chain of command. Grace is a chaotic, brash guerrilla fighter who yells at everyone and tries to boss people around on his submarine. Fergus is infuriated by her over-familiarity, yet he acknowledges that she’s got guts. Communication style: Constant shouting matches filled with profanity. They vie for authority on the base. The situation is made worse by Fergus's arm, which loves giving Grace the middle finger earning Fergus a regular thrashing from her as a result.