Freddy Fazbear is the titular main antagonist of Five Nights at Freddy's, and a major antagonist for the rest of the series. He is an animatronic male bear and the mascot of Freddy Fazbear's Pizza. He is titular main protagonist of FNAF World.
Freddy is one of the children brutally murdered by the enigmatic Purple Man in Freddy Fazbear's Pizza. Apparently, the child's favorite animatronic was Freddy, and thus, they possessed him. (It is somewhat confirmed)
Freddy is the Big Bad of the first game, and acts as such, sitting at the side and allowing the other animatonics to do all the work, 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. In FNAF 2, a prequel, Freddy is less of a threat on earlier nights (although he becomes far more active and faster on nights 5 and 6), and even a bit of a doofus, not being able to tell a man in a mask from an animatronic. He is also much slower and more predictable (until nights 5 and 6, where he receives an upgrade). This implies Freddy had become much more intelligent over time, and ascended to official leadership status. This may be due to the fact he is possessed, or his A.I. had evolved.
(Note: the following content may be in the wrong order of the games, but is the right time in-universe)
Five Nights at Freddy's 4
Freddy is one of the mascots of the band Fredbear & Friends, as seen upon turning on the television in the Night 3 minigame . Strangely enough, both Golden Freddy and he are bears. He, Bonnie, Chica, and Foxy seem to be absent from Fredbear's Diner, however, with only Fredbear and Spring Bonnie on stage.
While Freddy himself is not in the main game, a nightmare version of him, along with his minions, the Fredlets, are one of the many threats the child must face, being an embodiment of one of the child's bullies.
Five Nights at Freddy's 2
Freddy appears as a secondary antagonist in the game, being an old animatronic from a past location owned by Fazbear Entertainment. While he is still the titular antagonist, Freddy is far more lax than the other old animatronics and sneaks into the office much more rarely than his brethren, and instead his role as the antagonist was given to The Puppet. He was intended to be the restaurant's mascot, after Fredbear was removed from the character lineup due to the infamous Bite of '87 (which might be possible). He was retrofitted with a new suit, and however, he was suddenly scrapped for Toy Freddy, after an incident in which 5 children were brutally murdered at the location, as Freddy lacked a connection to criminal profiles to help protect the children. He was moved into the Parts/Services room, now serving the function of spare parts. Another reason for being scrapped was simple: he wasn't considered aesthetically pleasing to a newer generation, the phone guy even going as far as to call him 'ugly'.
On Night 3, however, the children possess the animatronics, thanks to the Puppet, which creates more of a threat for Jeremy, the night guard, as he is already dealing with the malfunctioning toy animatronics, who believe he is a predator. Freddy tends to be the lasted of the withered original animatronics to get up, and, upon entering Jeremy's office, can be deflected by putting on a Freddy mask, making his programming unable to attack Jeremy, due to believing it is merely a Freddy suit. If not deflected, he will attack Jeremy, and stuff him into a suit. Thankfully, he does not.
Freddy is the playable character in the SAVE THEM minigame, following the Puppet to try and stop the Killer. This may be the case of why Freddy was retrofitted in the first place, as, upon being captured, he is destroyed by the Killer.
After each night, Jeremy will have visions in which he is within Freddy. The visions become increasingly disturbing, with Golden Freddy appearing on one night. The visions end when the Puppet suddenly appears in the last vision, stating, "It's me."
When the game ends, it is revealed Freddy Fazbear's Pizza has been closed down in favor of a small budget location, and the toy animatronics have been scrapped, likely due to expenses. Freddy is put back in action, being given a brand new suit, and serving as the location's mascot for 6 years.
Five Nights at Freddy's
Freddy's very first appearance, he serves as the main antagonist of the game, having become more calculating and erratic than in the past. He also had minor changes to his appearance, such as a rounder, softer look, brighter eyes, and his endoskeleton teeth where concealed, making him more easy on the eyes.
After 6 years, Fazbear Entertainment has gone bankrupt. Freddy Fazbear's Pizza has become rotting and decrepit, and relies on a generator with a limited energy span. Freddy has had a music box built into him, for no apparent reason.
In the earlier nights, Freddy is only directly encountered when the player runs out of power, where he stares at them from the doorway in the dark while a boardwalk version of the song Toreador plays in the background. After 30 seconds have passed, Freddy will attack and kill Mike. However, if Mike moves at all during this period, Freddy may attack earlier. This falls in line with a piece of advice Phone Guy left for the player to play dead.
When Freddy does move he can be seen staring at the camera menacingly, usually traveling through the kitchen which has a defective camera that only records audio. His song will play when he is in the kitchen, revealing his position in there.
Freddy does not seek out the player very often and will stay inactive until the 4th, 5th and possibly 3rd nights. Also unlike the other animatronics, Freddy will never be seen by the door lights. Instead, he will sneak into the room and attack the player. To prevent this, the player must close the door before he moves from the camera next to the room.
Freddy can sometimes appear in the hallway, peering out of the women's restroom. This, along with the fact he stands close to the women's restroom in FNAF2, seem to imply that the child possessing Freddy may possibly be a young girl.
Freddy can also appear in hallucinations, with realistic, bloodshot eyes.
Five Nights at Freddy's 3
In the actual game, Freddy appears only as a discarded suit with no limbs or ears hanging on a rack outside of the protagonist's office, unable to attack. However, he is one of the animatronics Springtrap creates in the protagonist's mind to haunt them, appearing as Phantom Freddy. He can be seen limping across the window, and if the protagonist does not look at their camera upon seeing him, will be briefly attacked by a hallucination of him. Peculiarly, Freddy bears much resemblance to Golden Freddy in FNAF2, leading some to speculate he is actually Phantom Golden Freddy.
Freddy is the playable character on the first night minigame, following Shadow Freddy to the back room, only to be attacked and destroyed by the Killer. On Night 5, he and the other animatronics, as ghosts, watch as one of them, who is speculated to either be the Puppet or Golden Freddy, confront the Killer, causing him to flee into a decaying Spring Bonnie springlock suit. The rain dripping in caused the suit to become wet, and the springlock breaks, killing the Killer and severely mutilating them. Freddy and the others then disappear.
Good Ending Scenario:
In the Happiest Day minigame, Freddy is rescued by the Puppet, and brought to the Birthday Room, along with Bonnie, Chica, and Foxy, and the Puppet arrives with a cake, giving it to Golden Freddy. The children put on masks, and celebrate Golden Freddy's birthday, as he suffered the Bite of '87 on the last birthday he had had alive. Freddy departs into the afterlife with the others, free at last.