* Walt Disney World was a concept before specific characters: The idea of a Disney theme park in Florida was a dream of Walt Disney's, but he didn't live to see it realized. The first characters that were specifically designed for Walt Disney World were likely conceived during the planning stages, which began after his death in 1966.
* Characters evolved over time: Many characters, like Mickey Mouse, existed before the park's opening. As the park was being built, their roles and appearances might have been adjusted for the WDW environment.
* No single inventor: Characters were not invented by one person. Imagineers, artists, writers, and storytellers all contributed to their creation.
Therefore, there isn't one definitive "first character" for Walt Disney World. The park's characters are the result of a long process of development and adaptation.