Peterson "Peter" Löwenbräu-Justin Griffin Sr. is a businessman who hung himself. Steve Gerber found his corpse and unsatisfied with his own life, stole his identity, turning him into the man we know as Peter Griffin, today. He appeared in "Emmy-Winning Episode".
In the Breaking Bad parody of "Emmy-Winning Episode", Peter had a flashback to 15,768,408 hours earlier, (which led to the year 1965). In the 1960's, there was this big important business, run by Carter Pewterschmidt. Carter and his men were working on a way to sell alka seltzer. However, they needed to find some kind of slogan.
The men awaited a new business worker named Peter Griffin, who they planned on giving tons of money just for giving them a slogan. While they had this conversation, a lowly janitor named Steve Gerber, who worked just outside of the office and overheard the conversation and wished he could be the one making that money. Luckily for him, he saw that this "Peter Griffin" had hung himself in the next room over, unbeknownst to everyone else. After observing the scene, Gerber learned that Peter killed himself right then and there because just as he was about to enter the business room, he got a butt-dialed phone call from his wife, which revealed that she was cheating on him with another man.
Steve Gerber seized the opportunity to steal Peter Griffin's identity and take on his role. He went into the office, pretending to be Peter and he gave the big-name businessmen their slogan, earning himself a bunch of money. Since then, Steve has been keeping up this charade to the point, where he still identifies as the "Peter Griffin" we all known and love today and it wasn't until Joe figured out his secret, that we ever heard the name "Steve Gerber" again. Joe was willing to keep Gerber's identity theft a secret, as long as he got a cut of the money.