 Hader , who had previously cameoed in Monsters University , was cast to voice Fear , a role that he felt he " weaseled " his way into by being a " huge fan " of Pixar 's filmography . Hader toured the studio over a week , and also " helped out " in the story room . He was invited to play Fear by the end of his stay there , but was also asked to contact fellow Saturday Night Live ( SNL ) veteran Amy Poehler , whom the team viewed as perfect for the character of Joy . " They said : ' Would you mind calling Amy ? We don 't want to call her and have her think we 're some weirdo , ' " he recalled . He phoned Poehler and explained the story to her , noting that her role would be the driving force in the film . When the story was pitched to Kaling , she broke down in tears , explaining " I just think it 's really beautiful that you guys are making a story that tells kids that it 's difficult to grow up and it 's OK to be sad about it . " 
