Big Brother (Five Nights at Freddy's)

"Hey guys, I think the little man said he wants to give Fredbear a big kiss! On THREE! One....two...."

- Big Brother forcing his brother's head into Fredbear.

Big Brother (or "Foxy Mask) is a major antagonist in Five Nights at Freddy's 4, appearing as the main antagonist of the minigames. He is the protagonist's abusive older brother, and is the one who caused the child's accident. Nightmare Foxy represents him in gameplay.

Five Nights at Freddy's 4
Big Brother is only seen in the minigames, particularly on the second, third, fourth and fifth nights. His role as the child's brother, and not his father, is revealed on Night 5.

He hates his little brother, likely due to him still being a child, and has apparently abused the child to the point of him crying all the time. Five days from the party, he locks his brother in his room, laughing sadistically from the outside. Fredbear seems unfazed by what Big Brother is doing, only asking what he has done "this time." Fredbear constantly tries to help the child avoid Big Brother, guiding him with his words.

4 days from the party, the door is unlocked, but when the child enters the TV room, he jumps out from behind the TV with a Foxy mask on, making the child fall on the floor and sob.

2 days from the party, when the child enters his bedroom, he jumps out from under the bed, causing the child to fall to the floor and cry again.

1 day from the party, Big Brother and his friends lock the child in the Parts/Services room, the child banging at the door sobbing.

On the day of the party, the child's birthday, Big Brother and his bullies, wearing the masks of Freddy, Bonnie, and Chica, surround the child tormenting him, the one in the Chica mask commenting that the child is pathetic. Big Brother suddenly gets the idea to force the child to be right next to the Fredbear animatronic, the child screaming and shouting as he is dragged over to him. Big Brother decides to force his brother's head into the animatronic, saying that it's a big kiss to Fredbear. He underestimates the strength of the mechanical jaw, only laughing with his bullies as his brother's head is stuck. The child's forehead gets stuck between the second row of teeth, and the machine overpowers his skull, crushing through and ripping out his frontal lobe, causing Big Brother and the bullies to stop laughing and look in horror.

After the bite, something happens which causes the child to begin to die. Big Brother comes to his little brother's bedside, and apologizes in a brief statement. He had felt remorse for what he caused, and put himself on the path to redemption. It is unknown if he is a character met in the past games, leaving his fate ambiguous.

Personality
The child's brother is shown to be a sadistic trickster, who never cease to abuse emotionally and psychologically his brother. He seems to have no care about his brother's depression, as he torments him even in his own room. However, he is extremely remorseful for his actions as he came to his little brother's bedside, apologizing for his actions.

Trivia

 * Due to him no longer laughing upon seeing what happened, it is likely he feels remorse for what happened or horrified by the event.
 * Some people believed he was the child's father, before Night 5, where he is revealed to be the brother.
 * He is rarely thought to be one of the night guards, Jeremy Fitzgerald, Fritz Smith, Mike Schmidt, or the anonymous one.
 * He can possibly be seen as the Bigger Bad, with Fredbear being the main antagonist. Although Nightmare Foxy represents him.
 * Upon closer examination, the first three lines spoken in the Night 6 minigame, where the child passes on, are highlighted in grey text, revealing it is the brother at the child's bedside apologizing. The rest of what is said in the minigame, presumably belonging to the spirit within the Fredbear plushie, may or may not be the brother, with lines such as, "I will fix you." seeming rather strange for him to say.
 * Some suggest The Killer, being a witness to the Bite of '87, was angered by what had occurred, and murdered all four of the bullies, turning them into Freddy, Bonnie, Chica, and Foxy. Foxy specifically being the Brother. This would be a more dramatic turn of events if the rumor of the Killer being the child's father is true, as he would essentially be murdering his elder son. It would also cast The Killer's motive into a new light, portraying him as a Well-Intentioned Extremist.
 * However this is not confirmed.
 * Some people believe that the brother is Phone Guy, due to Phone Guy being nervous, working at the pizzeria for a very long time, knowing about the springlock suits and his favorite animatronic being Foxy (the brother wears a Foxy mask). However, the fact Phone Guy was an adult and worked at the pizzeria at 1987 and that the brother was a kid during the bite makes it impossible for them to be the same person  (unless the bite was not in 1987).
 * There is evidence pointing to  Five Nights at Freddy's 4 's events being a false lead for the Bite of '87 in the form of a TV screen broadcasting the date '83.
 * However, numerous fans have written out theories and connections that could disprove this.
 * He could be the anonymous one and his friends, the other bullies, think of themselves as a killer, anyways the brother and his friends have nightmares from what they did as seen in the other games.
 * It is theorized that he is Michael Afton, William's oldest son.