When "Snow White and The Seven Dwarfs" was released in 1937, it became the first ever full length animated movie - and it's generally accepted that Snow White, as the main character, was Disney's first princess.
However, just lately, there seems to be a body of opinion that this honor should be awarded to Persephone, who starred in a Silly Sympony entitled "The Goddess of Spring", which was released in the same year.
It's an interesting theory, but it doesn't really hold water. Persephone was a goddess rather than a princess (which a lot of people might think was even better).
The short Silly Symphony was, in fact, something of a trial run for the Disney animators. Up until that point. the majority of Disney characters had been animals - like Mickey Mouse and his various playmates. The Goddess of Spring was a good way to practice animating the human form in the realistic manner that would subsequently be required for Snow White.
So Persephone is not the first Disney princess - that is very definitely Snow White. Nevertheless. she played an important part in the development of the Disney magic.
Have a look at the 1937 Silly Symphony below. You'll see definite similarities between Persephone and Snow White.