Upon the orders of the First Elder, he was sent to eliminate the Japanese scientists involved with Unit 731: Naofumi Sakaguchi, Shigeru Takeuchi, Masaharu Shimizu, and Daisuke Nishibaba. 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. (TXF: "Nisei")
The RHM proceeded to find Dr. Ishimaru (a.k.a. Dr. Shiro Zama) on a train and killed him. He managed to obtain a passcode into a secure train car where an alien/human hybrid was being kept. There, he was confronted by Fox Mulder, though quickly got the upper hand. With the conductor distracting him and closing off the car, Mulder then got the upper hand and held RHM at gunpoint. The RHM convinced (or rather, deceived) Mulder he was from the NSA and that there was a bomb on the car.
The RHM got a phone call from the First Elder who had Scully with him. He handed the phone to Mulder and let them talk, Mulder finally asking the conductor to unhook the car in an underpopulated area, as the car was set to explode. The RHM said it was a mistake, and hesitated to answer Mulder's questions. With only minutes left into the car exploded, he finally led Mulder to believe 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?"
While Mulder was trying to key in the passcode to open the door with Scully's help, the RHM sneaked up and knocked Mulder out just as he was successful, then beat him. The RHM then got out only to be shot by X as he exited. The train car exploded soonafter. (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.