Rowena Ravenclaw was a witch who was born in the 10th century during the early middle ages. She founded the Ravenclaw house and took in the people who valued knowledge and wisdom. Shortly after Rowena had a daughter , Helena. Quite a few years later Helena stole her mother's diadem. Rowena kept it a secret for some time . Rowena fell ill and sent Baron (Bloody Baron , Slytherin house ghost currently) to find Helena so she could see her one last time. Helena , however , refused  and caused Baron into a rage in which he killed her. He then killed himself because he was overcome with guilt.So Rowena died with a broken heart and Helena and Baron became , as we know them today , Bloody Baron and the grey lady.