MIKE is an inhabiting spirit similar to the series' primary villain, BOB, who was his partner in serial murder. After committing several rape/murders with BOB, MIKE had a religious epiphany and repented, cutting off his own arm to rid himself of a "BOB" tattoo, which symbolized being touched by "the devilish one." BOB, however, would not repent. MIKE has spent years trying to find and stop BOB.
In contrast to BOB, MIKE only ever appears in the visual form of his host, traveling shoe salesman Phillip Michael Gerard.
After FBI Special Agent Dale Cooper comes to Twin Peaks to investigate the murder of Laura Palmer, MIKE appears to Cooper in a dream, explaining his and BOB's history, but in a way that is not immediately clear. He shows Cooper a vision of BOB as he appeared in life. Later, Cooper, Deputy Hawk, and Sheriff Truman locate Philip Gerard, who is at the time unable to give them any information. Later, in the show's second season, MIKE is key to solving Laura Palmer's murder.
In the prequel film Twin Peaks: Fire Walk with Me, during a scene taking place in the Black Lodge, The Man From Another Place confronts Cooper and asks, "Do you know who I am?" Cooper shakes his head, and The Man From Another Place responds, "I am the arm." This gives the indication that he is the arm that MIKE removed in order to get rid of the tattoo that linked him to BOB on the left shoulder.
MIKE also harasses Leland Palmer - BOB's host - in a road rage incident, where he accuses Leland of "stealing the corn," and that "The thread will be torn." At one point he addresses Laura saying "The look on her face when it was opened. There was a stillness like the Formica table top." Before driving away, MIKE tries to tell Laura that Leland is indeed BOB's host.