 The voice cast was signed on to do the film in 2001 , and work then began on the script . The producers were initially worried that creating a film would have a negative effect on the series , as they did not have enough crew to focus their attention on both projects . As the series progressed , additional writers and animators were hired so that both the show and the film could be produced at the same time . Groening and James L. Brooks invited back Mike Scully and Al Jean ( who continued to work as showrunner on the television series ) to produce the film with them . They then signed David Silverman ( who , in anticipation of the project , had quit his job at Pixar ) to direct the film . The " strongest possible " writing team was assembled , with many of the writers from the show 's early seasons being chosen . David Mirkin , Mike Reiss , George Meyer , John Swartzwelder , and Jon Vitti were selected . Ian Maxtone @-@ Graham and Matt Selman joined later , and Brooks , Groening , Scully , and Jean also wrote parts of the script . Sam Simon did not return having left the show over creative differences in 1993 . Former writer Conan O 'Brien wanted to work with the Simpsons staff again , joking that " I worry that the Simpsons @-@ writing portion of my brain has been destroyed after 14 years of talking to Lindsay Lohan and that guy from One Tree Hill , so maybe it 's all for the best . " The same went for director Brad Bird who said he had " entertained fantasies of asking if [ he ] could work on the movie " , but did not have enough time due to work on Ratatouille . The producers arranged a deal with Fox that would allow them to abandon production of the film at any point if they felt the script was unsatisfactory . 
