Question: is the movie spirit based on a true story

Answer: No, Writer John Fusco, best known for his work in the Western and Native American genres (such as the films Young Guns and Young Guns II), was hired by DreamWorks to create an original screenplay based on an idea by Jeffrey Katzenberg. Fusco began by writing and submitting a novel to the studio and then adapted his own work into screenplay format. He remained on the project as the main writer over the course of four years, working closely with Katzenberg, the directors, and artists.