pete docter started working on the script in 1996. he completed a draft treatment in february 1997 with harley jessup, jill culton and jeff pidgeon. however, sulley worked in the scream refinery before being changed to monsters inc.'s top scare producer. also boo was 6 years old, but was changed to 3 years. this was because "the younger she was, she became the more dependent on sulley," claimed by pete docter. the initial story did not have the character of mike wazowski. mike wasn't added to the story until in april 1998, when development artist ricky nierva drew a concept sketch of mike and everyone liked it. jeff pidgeon and jason katz story-boarded a test in which mike was helping sulley choose a tie for work and mike wazowski soon became a vital character in the movie. originally mike had no arms, and had to use his legs as appendages, however due to technical difficulties arms were soon added. billy crystal had been approached to play buzz lightyear in the original "toy story", but turned down the offer. however, once he saw the film, he regretted not taking the part, and when he was approached to play mike, he jumped at the offer. the film went into production in 2000.