Big Billy is a zombified gorilla that appears in the episode, "Reedickyoulus." He has brown fur and wears a small red hat that covers a piece of his exposed brain. He seems to be decomposed, as his foot is pure bone and chunks of his flesh are missing. He was bought by Meatwad in 2002 after he was tired of his hamsters dying quickly. Eventually, Shake shoved him in a microwave, ultimately killing him. Billy is able to communicate by using sign language.
In "Reedickyoulus", Big Billy and Meatwad's other pets rose from the dead and were resurrected, due to Carl's radioactive waste. He and the other undead animals try to take out their revenge on Shake, shoving him into a microwave. They fail to fit the anthropomorphic milkshake into the appliance because of his massive size. Big Billy then reveals to Meatwad that he wants to have sex, in order to turn him into a zombie. Meatwad declines, but Shake accepts this offer, fulfilling his desire to have free sex. Shake then has intercourse with the ape and is transformed into a zombie, declaring himself the "king of ape sex."