Upon the orders of the First Elder, he was sent to eliminate the Japanese scientists involved with Unit 731. He made use of his signature weapon, piano wire, to eliminate the Japanese diplomat Kazuo Sakurai, as well as to kill Dr. Shiro Zama's escort and Dr. Ishimaru (a.k.a. Dr. Shiro Zama) himself in similar fashion (TXF: "Nisei").
The Red-Haired Man managed to obtain a passcode into a secure train car where an alien/human hybrid was being kept. Confronted by Fox Mulder, he convinced (or rather, deceived) Mulder into believing that the being stored in the car was a weapon. He said to Mulder, "Ask yourself, my friend. What could be more valuable than Star Wars? More valuable than the atomic bomb or the most advanced biological weapons?"
After being distracted by a phone call, Mulder was beaten by the Red-Haired Man who escaped from the train car (which contained a bomb, ready to explode). As he exited, he was shot dead by X, who then proceeded to carry Mulder off the train car to safety (TXF: "731").
In the X-Files dvd collection, the Red-Haired Man's name is given as "Malcolm Gerlach", though he was never named onscreen.