What was the first Disney animated film that was not based on an already existing story?

The correct answer to this question is The Lion King. The animated film was released in 1994 and is regarded as a musical film. It includes an all star cast of notable names like Whoopi Goldberg, James Earl Jones, Matthew Broderick and Robert Guillaume. The movie tells the story of Simba who is to become King, after his father Mufasa, was killed by his father Scar.

The film was an instant hit, grossing $968.5 million worldwide and is the 46th highest grossing film of all time. The year it was released, The Lion King was the highest grossing film. In 2019, a remake was released including voices from Beyonce and Childish Gambino.