In PG Wodehouse's "Jeeves and Wooster" books and stories, Bertie Wooster has two meddling aunts named Dahlia and Agatha. It is possible that Dahlia and Hagatha are named after these fictional characters.
Actually, "Jeeves and Wooster" is a tv show originated in the 1990's and thus came out after King's Quest, and thus would have no inspiration on King's Quest's development. A more likely explanation for Hagatha comes from King's Questions that it may be inspired by the character of Aunt Hagatha from Bewitched. Although the name Hagatha for witches is generally fairly generic. As for Dahlia, more research would need to e made, but her first appearance in King's Quest as a name originates in about 1985 or so, in the second printing of the game.
Of course Wodehouse himself predates King's Quest, and so do the "Jeeves" books and stories. But there is still no direct indication that ties aunts to the concept of witches named Hagatha. Although the general idea of meddling aunts does exist in Bewitched as well, as Aunt Hagatha does hang around with Aunt Enchantra.Baggins (talk) 23:22, December 26, 2014 (UTC)