Betty

Betty was one of the more unique antagonists in the X-Files, a "Monster of The Week" she was not so much a physical being as a split-personality of sorts to another character, though due to the paranormal nature of the show much of Betty's nature was left to the viewer's imagination.

Bio
Betty was the name of a tattoo received by Ed Jerse. She appeared as a vaguely sinister winking woman with the words "Never Again" written below. Scully learned that the brilliant red dye on Betty's lips contained a hallucinogenic compound that made Jerse believe he could hear Betty "speaking" to him. Betty constantly attacked his self-esteem and prompted him to explode at his coworkers and murder one of his apartment building neighbors. Upon meeting Scully, Betty became very jealous and nearly succeeded in convincing Jerse to kill her, too. Jerse, however, was able to overcome Betty's influence and thrust his arm into the building's furnace, burning off the tattoo.