Manuscript evidence suggests that Chaucer initially assigned the Wife of Bath a different tale, probably what is now the Shipman's.
In older, mostly Celtic versions of the loathly lady folktale motif, the loathly lady represents the sovereignty of Ireland. The hero of the tale must marry her in order to become high king. (Source)
Chaucer's "Wife of Bath's Tale" was the inspiration for a later anonymous British romance called The Wedding of Sir Gawain and Dame Ragnell.