The Vulture is a character that was originally created for Sleeping Beauty but was deleted during the film's production. Originally, Maleficent was going to have a pet vulture, which was meant to serve as comic relief (very similar to Iago) and had a New York accent. However, because his role did not contribute much to the story and also somewhat detracted from that imposing nature of Maleficent, he was cut from the final version of the film. Despite this, there was dialogue written for the vulture and some rough sketches for the character.
After the vulture was removed, Diablo was created to fill the role of Maleficent's pet and confidant.