Whedon has said that while the basic structure of Toy Story was solid, when he came on board the script simply didn’t work. Buzz and Woody were sarcastic and spiteful characters that audiences simply wouldn’t be able to connect with. Whedon tried and failed to make Barbie a part of the story, that character would appear later. He is, however, credited with creating the dinosaur Rex, as well as coming up with the idea that Buzz Lightyear, being a new toy, doesn’t realize that is a toy, and thus believes he actually is a Space Ranger.
Article source: https://www.cinemablend.com/news/2475770/yes-woody-has-a-last-name-and-4-more-toy-story-facts