Board Thread:Wiki-Related Discussion/@comment-929837-20141109085917/@comment-5106672-20141117153739

Regina IS based on the Sea Witch from the Little Mermaid fairytale in that she assumes the role the Sea Witch had in said fairytale: tricking Ariel into giving up her tail for legs, and then taking away her voice.

The fact that there is The Real Ursula out there, and that she is based on the Disney version, doesn't change the fact, because, as I always like to remind people, Disney movies ≠ source material fairytales.

Side note: the fact that two characters are based on a single one is not surprising: both Anna and Gerda are based on Gerda from the fairy tale, and both Elsa and Ingrid are based on the Snow Queen. But if we want to dig deeper, both Aurora's Mother and Aurora herself are based on the Sleeping Beauty, both Cora and Cinderella are based on the Miller's daughter (because Cinderella functionally got the Miller's Daughter's role in The Price Of Gold) and so on.