Jerry Smith, also known as Yellow Guy, is the man who originally designed Freddy, Bonnie, Chica, and Foxy after the FNAF2 Pizzeria closed. Having a rare case of jaundice, his skin and eyes are permanently yellow, and so is his shirt. He wears black shoes and pants as well.
An engineer who worked on the original animatronics at Fredbear's for a short time, Yellow met Purple Guy while working on an animatronic. At first, the two got along fine, but then Purple threatened to kill Yellow's sister, also engineer at Freddy's, if he didn't carry out his murders for him. Complying, Yellow secretly murdered 12 people and hid all the bodies in animatronics.
The killings were in vain, though; Purple had murdered her even before Yellow began his slaughter. In misery, Yellow quit his job and started working as a full-time night guard. Eventually, 6 years later, Jerry was asked again to redesign Withered Freddy, Bonnie, Chica, and Foxy. Accepting the job, he fixed all the animatronics, and programmed them with one simple command. Kill anything in purple.
Eventually, 20 years later, Fazbear's Fright reopened, and Jerry helped find relics for the attraction. Remembering the back room he was in when he met the Purple Guy, he looked inside the room and found Springtrap. He later discovered Purple was inside of Springtrap, and out of vengeance, he lit Fazbear's Fright on fire, knowing Purple wouldn't survive and it would all be blamed on faulty wiring and ventilation.
Yellow seems calm and composed, and not afraid of anything, even death and being stuffed into a suit. He never got over his relative's death, though, and he is really a bitter, angry man.
Purple Guy: Goes without saying he hates everything about him.
Chef: They seem okay with each other; both are simliliar in fates; Chef was a stuffed human, and Yellow had someone he loved stuffed.
-Yellow has worked the night guard job a lot, and it shows: He has an endoskeleton arm, batteries duct taped into cuts, bandages, blood stains on clothes, etc.
-His right arm was bitten off by Foxy; for revenge, Yellow took Foxy's arm.
-Yellow Guy's name comes from the jaundice he has; in addition, he always wears yellow, and originally designed Golden Freddy.
-His sister may have been the writer of this journal.
-A rare hallucination may be attributed to him; if you run out of power in FNAF1, rarely a Golden Freddy will appear at the door, with discolored eyes appearing out of it. Some speculate this is Yellow in Golden Freddy, though reasons for him wanting to do this are unknown.