The Banshee is a minor villain in Darby O'Gill and the Little People. She takes people who have died to the Otherworld while letting out a horrible wail. She's the one who took Darby O'Gill's wife away years ago and she almost took Katie after she fell from the mountain of Knocknasheega for trying to fetch Cleopatra, the horse but failed thanks to Darby throwing a lantern at her. But she wasn't giving up; she tried again at Darby's house and to get her once and for all, she summoned the mystical Dullahan driving the cóiste-bodhar (the Death Coach) to carry her soul off to the land of the dead when Darby tried to shoo her away with a shovel.
Desperate, Darby elected to use his final wish to go in his daughter's place from King Brian. King Brian was deeply saddened at Darby's wish but granted it, but once Darby was on his way to the next world, King Brian reappeared in the Death Coach and tricked Darby into making a final fourth wish ("wishing" that his friend could join him in the afterlife). Because he was only allowed three wishes, this negated all the previous wishes and spared Darby's life. Darby was saved and King Brian had (literally) the last laugh in their running battle of wits.
In Irish legend, the Banshee is often said to be seen combing her hair as she approaches. Although the Chroma Key technique makes it difficult to see, the Banshee that comes to Darby is indeed combing her hair.
The Banshee's wailing can be heard in various media related to The Haunted Mansion, most notably the ride itself, the Story and Song record album, and the Chilling, Thrilling Sounds music album.