Jack has blonde hair that is shaved to almost bald and green eyes. He is very muscular and had brutish pig-like features along with pointed ears (Frank Mathers looks similar to him).
Jack wears a brown polo shirt with the logo of the Hamlin Battalion at the back, half-pants of regular Hamlin Battalion soldiers design (hence, there is no knee pads) with a black utility belt to his waist and green combat boots. Said utility belt is attached to his upper body by suspenders. He also wears a dark blue lieutenant hat and brown gloves. As for equipment, there are numerous case boxes on his utility belt and there is a case box on his both pant legs. He has a device which prevents the Terror Bites from attacking him on his neck. As for weapons, he is armed with a two-barreled machine gun, Mk 2 hand grenades and uses Mantis Terror Bites. Even with occasionally disarmed by Captain Rush, Jack is an expert wrestler and is able to defend himself in unarmed combat even a large chunk of wooden crate did not work against him.
Mathers was once a hero in the past and extremely loyal to America. Serving Gregory Barrows, Mathers does not always listen when it comes to certain tasks (since he tends to be a fanatic type). Knowing that Barrows' orders are absolute, Mathers vows to listen and communicate with Barrows more closely. He is sent to guard the Biological Weapon Research Facility in Wyoming against those who oppose Barrows. It is unclear whether he died after the battle or merely fell unconscious and was arrested later. However, judging by the weakening of his voice, it could be assumed that he died after getting shot many times by the V.S.S.E.agents (weakening him) and punched by Captain Rush (effectively killing him).
His hairstyle is similar to that of his namesake, the Jack robots of the Tekken series of fighting games also created by Namco, especially to Gun Jack.
He is the only Antagonists that can talk while fighting, notably the player can shoot him when he is fighting Captain Rush but is unable to decrease his lifebar (the latter trait is first used by Giorgio Zott on his final lifebar).
He, along with Wild Fang, is a boss that was not finished by shooting down to death (Jack Mathers was finished by an uppercut from Captain Rush).