Bonnie

Before becoming Bonnie, he was named Jeremy who attended a birthday party at a Freddy Fazbear's Pizza. However, William Afton disguised as Spring Bonnie, lured him and four more children into the backrooms from the restaurant where he murdered them and hid their bloodied corpses inside soon-to-be-released animatronics, including Freddy Fazbear. The children's spirits remained trapped in the animatronics. When the animatronics were released, parents were quick to ask about blood and mucus oozing from their eyes and mouths; and deemed the animatronics too creepy and smelly, causing the restaurant to close down.

Soon the 'new and improved' Freddy Fazbear's Pizza was opened, starring new versions of Freddy and Co. based on the creepy animatronics, known as the Toy Animatronics. The old ones were kept for parts, and would come to life at night, with unknown reasons causing all the other animatronics to do the same (with the exception of the Puppet, who was seemingly constantly sentient throughout the day and night). Every night they attacked the night guards, hoping one of them would be the man that destroyed their lives.

Eventually this pizzeria was closed down after somebody used one of the 'yellow suits' once again for sinister purposes, and was replaced a few years later with yet another pizzeria of the same name, this time only using the original animatronics (with modifications to their designs to improve upon the original scary appearances). They still attacked the night guards, just as before, and their behavior continued until the pizzeria closed for good after its popularity reached an all-time low.

Years later, the original murderer returned to Freddy's, and destroyed the animatronics, thinking that would stop them from hunting him down. Instead, he unwittingly released the spirits of the first five children he murdered, who converged on him in the pizzeria's Safe Room. In terror, he hid in the same Spring Bonnie suit he had worn decades earlier. Despite thinking he was safe, the suit's age caused it to malfunction and kill him, allowing the spirits to leave the animatronic bodies. Eventually, the five spirits met once again alongside the spirit of the Puppet on the Happiest Day, where they were officially released from their animatronic personas and could finally be at peace.

Normal
Bonnie is a tall animatronic who looks like an anthropomorphic, dark-blue bunny, with two longs ears, albeit not sufficiently proportioned to his size.

Damaged
In the second game, Bonnie's appearance is much more frightening, as his face has been scouped out, and his two red endoskeleton eyes peering out of the depression where his face used to be.

He has two buttons added to his chest and is also the most damaged of all the older animatronics. His face has been gutted while his lower jaw remains, featuring more teeth than he possesses in the previous game as well as glowing red irises.

His left arm is missing entirely, with a mass of wires in its place. His suit has become tattered, particularly around the legs, and a few loose wires poke out of his body.

The covering on his right hand and his entire left arm has come off, revealing his endoskeleton and wires. He also seems to have a bigger stomach than before, as it looks more rounded and bigger than his upper body.

His chin also doesn't squash his bow tie now. It is explained that the management tried to have Bonnie and the old animatronics retrofit but this was scrapped in favor for the newer, toy models.

The day, Bonnie appears as a friendly, harmless, joyful, nice and sympathetic robot, who never harm children and always take care of them, often playing guitar along Freddy and the rest of the gang to distract customers of the restaurant; albeit his appearance is somewhat disturbing, and his behavior rather malevolent upon confronted to adults.

Once he is confronted to the night guard, Bonnie turns into a cunning, malicious, merciless, evil-minded, rather impatient murderous stalker, obsessed by the idea of stuffing the night guard into an endoskeleton for some dark reasons.

Bonnie is the smartest and second most dangerous - behind Foxy - of the animatronics. If he waits outside the door, it isn't for very long, although if he is far from the office, he can travel there surprisingly quickly. Shutting the door on him wears him out quickly into leaving, as opposed to the persistent Chica. He is also the first to leave the stage.

One of his dirtiest tactics is to hide in the storage closet, and bound to the office at an incredible speed, and catch Mike off guard.

He is very unpredictable and possibly impatient as he twitches constantly on Night 3, indicating he might be getting frustrated. Bonnie is, in fact, possessed by the soul of one of the child killed by William Afton, which explains his temperamental and evil behavior.