Betty Boop, a caricature of the original Boop Boop a Doop Girl,
Helen Kane, began life as an unnamed character in this Talkartoon. She was created to appeal to the Fleischer studio's current canine star, Bimbo. By 1931, Betty had become human, while Bimbo remained more or less a dog.
Source:
Leonard Maltin, Of Mice and Magic: A History of American Animation, NY, 1987, p. 100