According to Hader in an interview with IndieWire, naming the character “Toro” was an explicit attempt to secure Guillermo del Toro’s acting services.
“Guillermo sent me a funny text [asking], ‘Could I be in Barry?’ People say [they want to be in the show] sometimes, and it never happens. But then I thought, ‘Actually, there’s a part that he’d be really good in.’ I called him and said, ‘Yeah, I have a character for you. His name’s Toro.’ And he went, ‘Oh, man. Really?’”
The Mexican director is best known for his love of monsters and practical effects as seen in films such as Pan’s Labyrinth, The Shape of Water, and Guillermo del Toro’s Pinocchio. While not an actor by trade, he occasionally finds his way into brief guest appearances in TV shows and movies he’s a fan of, as previously evidenced by his role as Pappy McPoyle on It’s Always Sunny in Philadelphia.
Per Hader, del Toro brought his own cane to set and impressed production with his character’s subtle but increasingly agitated reactions towards the disparagement of his employees’ podcast.
“[When] we were in the editing, we realized the funniest part about it was just watching him react,” Hader told IndieWire. “When we would watch his full takes, the way he was reacting was making me laugh really hard.”
While casting del Toro to play a monstrous murder broker named El Toro is funny enough, the real punchline to the director’s appearance doesn’t land until the arrival of the second guest star. In the episode’s final act, Barry Berkman notices a supposed FBI agent covered in sweat and visibly shaking and quickly and correctly diagnoses that the guy is here to kill him. The guy isn’t so nervous because he has to kill another human being necessarily but rather because he’s armed with one of Los Amigos Gadgets’ potentially malfunctioning gadgets.