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In the 2013 Disney-Pixar film "Monsters University," Charlie Day plays Art, a "New Age Philosophy" major and member of the Oozma Kappa fraternity. The film was a prequel to the 2001 feature "Monsters Inc.," both films exploring a world built and inhabited by sociable monsters who live out of the ordinary lives.

When Day was offered the part, he wasn't given much information about the project or the character — according to him, they simply asked (via Collider), "Do you want to be in a Pixar movie?" "I think they understood the leverage that they had because I said yes, immediately," Day said of the experience.

The actor's first animated Disney film, Day was excited to join the Pixar pantheon of voice actors. "I've always wanted to do it. I always love hearing Tom Hanks, John Ratzenberger, Billy Crystal, John Goodman, and all of these wonderful actors doing such great performances," he told Collider. He went on to say that during his first meeting with the studio about the character, they had animated Art to voice clips from "It's Always Sunny in Philadelphia," giving him a clear picture of what the creators wanted. 

Director Dan Scanlon described Art (via The Pixar Times) as that "college guy you don't know anything about." Day himself theorizes that Art isn't even going to Monsters University — "I have a suspicion that he's not actually a student at that college. He's a drifter. He might have gotten off the railroads and wandered into Oozma Kappa," he told Collider. Day also voiced Art in the 2014 animated short "Party Central" and the "toys-to-life" game "Disney Infinity."