Ash and his friends heard the legend about how, over 2,000 years ago, the young woman's lover was sent off to war, leaving her desperate for his return. Though the days faded to years, the maiden refused to give up hope and eventually had her body bonded to the peak upon which she stood. Nowadays, the young woman's soul is said to still yearn for her lost love. At some point, a Gastly decided to keep her story alive and posed as her so it could commit mischief.
According to the legend, she is notorious for stealing the hearts of young men, putting them in a trance-like state and stealing them away from this world. This seemed to be demonstrated on Brock and James, but Ash, Misty, Pikachu, Jessie, and Meowth eventually realized it was Gastly's doing.