He appears as the central antagonist of Five Nights at Freddy's: The Silver Eyes, a supporting protagonist in The Twisted Ones and The Fourth Closet, and a cameo character in Fazbear Frights.
In the original trilogy
Freddy Fazbear was one of the animatronics Henry Emily created. Charlie first saw him deactivated inside his dad's house. On July 1985, a kid was kidnapped by William Afton, dressed with a golden suit, and stuffed inside the bear's suit.
Five Nights at Freddy's: The Silver Eyes
In 1995, after breaking inside the pizzeria, Charlie and her friends discovers that Freddy and the other mascots were left behind. When they come back once again to the pizzeria, Freddy, together with Bonnie, Chica, and Foxy try to attack them, but he's stopped by Golden Freddy, possessed by Michael Brooks, a childhood friend of Charlie.
Five Nights at Freddy's: The Twisted Ones
In this novel it's revealed that, after the events of the first book, Chief Burker took the bodies out of the animatronics, damaging them in the process, and that he keeps them in the basement. After hearing that William Afton is still alive as Springtrap after being stuffed inside the SpringBonnie's suit, they reach the Twisted Animatronics, created by William to find and kill Charlie, and they starts to fight against them. During the battle, Freddy defeats the Balloon Boys who where attacking Charlie's friends.
Five Nights at Freddy's: The Fourth Closet
In this book, it's revealed that William Afton melted together the original animatronics' endoskeletons, including Foxy's one, to create an animatronic known only as The Amalgamation, where he wants to transfer his consciousness to become definitively immortal. When Carlton Burker, who was injected with remnant, enters in the spiritual world, he meets an unnamed young boy with brown hair, who possesses Freddy. After William is pushed into a furnace by the funtime animatronics, who rebels against him, all the trapped souls are finally able to pass on.
In the Fazbear Fright's Short Stories Collection
Freddy makes various short cameos through the Fazbear Frights' stories.
Into the Pit
He appears in Into the Pit when Oswald travels back in time using a ballpit, coming back to 1985. Freddy's one of the animatronics on stage, together with Freddy and Bonnie-
In Fetch, the protagonist Greg finds four deactivated adult-sized animatronics behind the show stage's curtains. Despite this has not be confirmed, it's possible they are the original Freddy, Bonnie, Chica and Foxy.
While Freddy Fazbear doesn't physically show up in this story, the Lonely Freddy toy line is based on him.
The New Kid
When Devon, Mick and Kelsey explore an abandoned Freddy's building, they find Freddy deactivated on the stage, and various drawings of him on the walls.
Freddy shows an aggressive behavior towards adult people, thinking they are his killer. As a kid, he seems pretty shy and introvert, not even talking with Carlton when he meets him.