Peter is a giant pig altered by Ms. Frankie, Matthew, and Roland, who were all wearing Solar Opposites masks during his creation. He was introduced in the episode "The Apple Pencil Pro". He self-cooks racks of award-winning ribs out of his chest and his blood tastes like delicious barbecue sauce. When struck, Peter will "shit out all the fixin's."
Peter was too sentient for this to be an ethical practice. He escaped from the three of them. He spent a few nights in the woods, then he moved on with his life. He got his MFA in interpretive dance, but could not find work related to that field. So, he got a job at the Apple Store.
One day, when The Solar Opposites were in the Apple Store, Peter spotted them. Because of the masks that Ms. Frankie, Matthew, and Roland were wearing, Peter believed that the Solar Opposites were the ones who tortured him. He decided to file a lawsuit against them.
Since the Solar Opposites were framed, they pleaded innocent in the case, but were found guilty on all counts. They were sentenced to put on gloves filled with Brazilian Bullet Ants.
Peter himself seems completely oblivious to the truth of his creation.