Based on the Freddy Fazbear's Pizza theme song, during the day, Freddy loves to have fun and is also shown to be laid-back, easygoing, and happy-go-lucky.
However, during the night, Freddy is shown to be taunting constantly, laughing at the night guard and playing a song before triggering a jumpscare. He is also shown to be sneaky, as he moves in the shadows towards the night guard and even manages to slip through the door quietly without the guard noticing. This reveals a darker and taunting side of his personality.
In Five Nights at Freddy's AR: Special Delivery, Freddy gets a new voice, one that is very deep and a bit glitchy. Freddy is shown to be openly malicious, taunting, and loves to scare his victims, but some of his lines suggest that he is somewhat merciful. Overall, Freddy is shown to have a childlike sense of mischief and sadism.
As Withered Freddy, nothing much is known about his personality. However, Withered Freddy shows that Freddy has a benevolent side, as it's shown in Five Nights at Freddy's 2 that he appeared to be protective of children as he tried to save them from his killer, William Afton, in the SAVETHEM minigame; however, he was too late.
With similar technology to the funtime animatronics that allow costume plates to be opened immediately, Freddy's bow tie allows the torso to open when the button is pressed for easier access to the innards. His endoskeleton includes a safety latch, which is a strange metallic black and yellow wire that can extend a metal bar to lock it in place. Freddy's endoskeleton features a red button that powers said safety latch. Freddy's music box is tucked safely to the left of Freddy's endoskeleton.
Since the reveal of the final image of Freddy Fazbear's Pizza Simulator, it has been heavily speculated, but not confirmed, that the name of the child possessing Freddy Fazbear is Gabriel. Since the reveal of the final screen of the Lore-keeper ending in Freddy Fazbear's Pizza Simulator, that the child (based on the position of Freddy's head in the Good Ending of FNaF 3) possessing is heavily hinted to be Gabriel further supports this. In the Fourth Closet novel, the child that possessed Freddy was an unnamed boy.
In Five Nights at Freddy's VR: Help Wanted during the end of the Pizza Party level, Glitchtrap lures the player to the backstage with a cake. After that, the player becomes Freddy and watches Glitchtrap as he dances to the song. It theorized that this was the moment the child was killed and stuffed inside Freddy. Since the cake has seven candles it, is theorized that the child was seven years old.
As the mascot of the restaurant, the day Freddy appears as a nice, joyful, and lovely mascot who takes care of customer's child and always trying to cheer them up, as expected from an animatronic. However, once he is alone in the dark, he turns into a cunning, dangerous and malevolent robot, willing at all cost to catch and stuff the security guard into an endoskeleton suit. The reason for this behavior is that the animatronic is, in fact, possessed by the vengeful spirit of a child named Gabriel who was murdered at Freddy’s (c.f. History).
Freddy is the original leading antagonist of the first game, and acts as such, sitting at the side and allowing the other animatronics to do all the work in the earlier nights, and when they fail, he finally comes into action himself. In FNaF 1, he is very intelligent and strategic, and also presumably the leader of the gang. If the power runs out, he always is the first to enter the office, even if he is the animatronic furthest from said office, meaning the other animatronics may be allowing him the privilege (as leader) of getting the night guard. However, even if Freddy's AI is set to level 20 on Custom Night, he won't move until Bonnie and Chica have left the Show Stage.
When on the move, Freddy lets out a very deep belly laugh that echoes throughout the building. Like the other animatronics, Freddy appears to be a sadist, toying with the night guard in order to break him mentally, and laughing at his misery, although he is still not completely evil for many reasons. That, and he plays his music before killing the guard if the place runs out of power, leaving the guard in complete and utter fear, not knowing when he will be killed. Freddy may be a mutilator as well because once the protagonist is killed, his eyes and teeth are shown through the openings of the suit, with the former's eyes popped through the suit's eye sockets and teeth showing within the mouth of the suit. In the second game, Freddy appears in the Game Over screen and the point of view is from inside the suit.
Despite being a violent and sadistic animatronic, Freddy attacks only because he wants to avenge himself and his friends by killing their murderer. However, he doesn't know how his killer looks like, all he knows is that he was a night guard (heavily implied by the SAVE THEM minigame), explaining why he's so hostile to them. He also seems to be protective of other children not wanting them to die like he did he even teamed up with the Puppet in the SAVETHEM mini game to rescue Afton’s victims although unfortunately he was too late.
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