"Purple Guy" is the unofficial name given to a recurring character from the Five Nights at Freddy's series. He is a child murderer whose victims include the unnamed children whose souls currently haunt various Freddy Fazbear's Pizza locations: specifically, the animatronic costumes legend says the Purple Guy had stuffed their bodies into.
While the Purple Guy does not directly antagonize the player character, his past actions have resulted in the events that led up to the games' main stories and are recreated in a series of mini-games that play in-between levels. In the mini-games featured in FNaF 3, we learn that after being confronted and cornered by the ghosts of his victims, the Purple Guy was killed by a malfunctioning Bonnie mascot suit--officially referred to as Springtrap--which crushed him to death as he he attempted to wear it.
Despite numerous fan theories, the identity of the Purple Guy is officially unknown.