Sringtrap is a heavily-damaged Animatronic / Springlock Suit that carries the reanimated corpse of Purple Guy in his insides after the Springlock accident in Freddy Fazbear's Pizza I.
Five Nights at Freddy's 3
In Five Nights at Freddy's 3, Springtrap comes back to "Fazbear's Fright: The Horror Attraction" seeking revenge, for unknown reasons, against the Night Guard. In doing so, Springtrap awakes the Phantoms of the Animatronics from Freddy Fazbear's Family Pizzeria I and II.
When Michael Afton came back to the first Pizzeria to dismantle the old Animatronics due to maintenance questions, involving the complaints of Jeremy Fitzgerald (Night Guard) about the attractions appearing to act as if tried to penetrate in his office and potentially "hurt him".
However, when Michael dismounted the Animatronics, they fought back and managed to corner him in a closed Parts and Service room, where the only thing he found was two Springlock suits. Michael quickly wore the Spring Bonnie suit, managing to hide from the robots. When Michael breathed relievedly, he accidentaly collapsed the Springl ocks, causing the Suit to smash and brutally murder him. After hearing of these Springlock accidents, the owner of the Pizzeria's robots, William Afton (father of Michael and owner of Afton Robotics) has ordered to swap them to Parts and Service and replace them with newly-built Toy Animatronics, wielding a much "cuter" and attractive personality for children public.
Springtrap acts in a surprisingly human way, being able to walk into all places and rooms towards the building and using the Phantoms simply as distractions to gain time to murder the player.
He is also the only Animatronic in Five Nights at Freddy's 3 capable of actually killing the player and giving him a Game Over screen because the Phantoms can simply project themselves to scare the player, endark the screen, and cause different types of Errors in the system. It is possible for them to kill the player, however, if on Night 4, on Medium, Hard, or V. Hard modes, they can kill you if they cause a Jumpscare streak. However, the player's biggest worries is still about Springtrap penetrating in your office through the Left (Doorsteps) side, or Right (Ventilations) side.
If the player plays the Audio (possibly registered from Balloon Boy from Five Nights at Freddy's 2), Springtrap has a certain chance depending on the Night and Difficulty of the level, to follow to the room the player chooses.
Similar to the Nightmares from Five Nights at Freddy's 4, Springtrap is a heavily-damaged robotic Rabbit. That because he is a damaged Springlock suit that corresponds to Spring Boonie, from Fredbear's Family Diner.
It is possible to see part of Purple Guy's red-colored skull from the inside of Springtrap when he opens his robotic jaw. It is also exposed like wiring from the holes that expose his insides. Since the suit is empty due to being Springlocked, it has proven that the eyes from Springtrap's face also belong to Purple Guy's corpse.
Five Nights at Freddy's: Sister Location