Parrish was first hired by Disney as animator for Alice in Wonderland (2010), before moving onto animating for Tangled, Wreck-It Ralph, and Big Hero 6.
In an interview, he described how he was drawn to the the film because the relationship between Hiro and Tadashi reminded him of his own relationship with his older brother.
He was the lead animator during pre-production on Go Go because he felt like he could relate to her, and liked the contrast she brought to the team, being such a calm and collected character who also had the ability to do outlandish physical activity where they could push the Marvel dymatics of the film.
He also talks about how they went about designing Baymax's face. They considered giving him a mouth or eyebrows, but decided that he was well designed enough that the audience would understand him from the phrasing of his dialogue, and from small motions such as blinking or tilting his head.