Nightmare Fredbear is one of three main antagonists of Five Nights at Freddy's 4 alongside the Big Brother of the child and his own enigmatic counterpart Nightmare. While he first appears to be helping the child protagonist, it is later revealed that he is the embodiment of the child's fear of the Fredbear animatronic, as he was directly harmed by the animatronic. It's very possible that Fredbear was in fact the one that caused the Bite of '87.
Fredbear is a golden bear with a purple hat and bowtie. Just like the other animatronics, he is extremely withered. Some perceive that he has a second mouth located on his chest. The second button on his chest appears to be its nose, with two holes being its eyes. Others believe this to just be decayed suit with animatronic framework underneath. He has teeth extremely similar to Nightmare Chica.
Five Nights at Freddy's 4
Fredbear is the main antagonist of the actual gameplay of the game, being the child's root fear. The animatronic itself is what bit the child, thus making the child envision him as the Big Bad. The child sees him as far more dangerous and terrifying than his own Big Brother (which he is in a sense).
In Night 5, all of the nightmare animatronics mysteriously disappear, with Nightmare Fredbear appearing everywhere they do, and doing each of their jobs, however, as there is only one of him, he is the only threat. However, he is quicker, and more difficult to get rid of, constantly laughing sadistically throughout the night.
After the night is completed, the next mini-game shows bullies, including the child's brother, picking on the crying child, then, as a cruel joke, put the child's head in the mouth of the Fredbear animatronic, causing it to be unable to sing. The child's forehead became trapped between the second row of teeth in the animatronic, and, as the jaw slowly clamped down on his head, the bullies laughed. Their laughing soon turned into horror, as Fredbear's jaw suddenly broke through the child's fragile skull.
On Night 6, at exactly 4 am, all of the animatronics disappear, and are once again replaced with Nightmare Fredbear. The child defeats Nightmare Fredbear once and for all, and the nights of nightmare end.