A Yamauba is a particularly powerful and evil yokai hag from Japanse folklore that frequented mountains and forests, envisioned as hideous old women they often could not be truly distinguished as monsters until it was too late and delighted in hunting down humans both as prey and for sheer sport.
Yamauba were thus in many ways the "wicked witches" of many Japanese folk tales and were said to be the result of evil-minded women who dedicated their lives to black magic, thus they became man-eating hags and often disobedient children were warned to improve their behavior or face the risk of a Yamauba coming to spirit them away (acting much like the bogeyman in other cultures).