It's Always Sunny: Which Episodes Star Guillermo Del Toro And Who Does He Play?

With their outsize affection for lukewarm milk, family hooplas, and, uh, each other, the McPoyles are some of the biggest oddballs to emerge from the "It's Always Sunny in Philadelphia" universe. Odder still is that renowned Mexican auteur Guillermo del Toro plays the McPoyle family patriarch, Pappy.

Pappy made his triumphant debut in Season 8, Episode 3, "The Maureen Ponderosa Wedding Massacre," in which the McPoyles gather for the wedding of Maureen Ponderosa and Liam McPoyle. In the Season 11 episode "McPoyle vs Ponderosa: The Trial of the Century," the wedding party — including Pappy — reconvenes to hash out the disastrous occasion in court.

The Oscar-winning director was happy to debase himself for his good friend Charlie Day. "I told Charlie to give me the most demeaning cameo he could in the episode, and he came up with Pappy McPoyle," del Toro said in a behind-the-scenes interview. The filmmaker plays Pappy with the unhinged exuberance of a man who spends most of his time behind the camera, rambling incoherently about eating his children. "Pappy McPoyle is like Zeus," del Toro tongue-in-cheekily proclaimed. "He is the originary father of all the McPoyles. They come from his loins like the Titans in Greek mythology. And he has to destroy them before they eat him."

Not everyone would be willing to play a lunatic patriarch of inbreds on "It's Always Sunny," least of all a venerable filmmaker. Such is the friendship between Guillermo del Toro and Charlie Day. The pair first worked together on del Toro's 2013 cult favorite "Pacific Rim."

For Day, "Pacific Rim" was eye-opening — so much so that he tried to incorporate some of del Toro's filmmaking techniques in the horror-inflected "The Maureen Ponderosa Wedding Massacre." After getting the preliminary shots, Day asked director Richie Keen if they could do what he described to Conan O'Brien as "a few Guillermo takes." That inspiration has persisted on "It's Always Sunny," the episodes of which have become more experimental and ambitious over the years. "[We] just started using more, as I called them, 'Guillermo takes' throughout the show, and just getting more and more inspired to do more filming and make more things."

Del Toro has continued to be instrumental in Day's filmmaking journey, even giving Day notes and guidance for his directorial debut, "Fool's Paradise." "I owe a massive debt of gratitude to Guillermo Del Toro," Day told The Hollywood Reporter. "I would send him pages, and he would send them back with his notes. But he really helped guide me, and he gave me the confidence to just go ahead and do this reshoot."

With Day and del Toro seemingly tighter than ever, it's not outside the realm of possibility that Pappy McPoyle will rear his bird-wearing head on "It's Always Sunny." The trailer for Season 16, which premiered on June 7, even promised a grand McPoyle return.