The Night Mother is the spiritual leader of the Dark Brotherhood and resides in a crypt below the Lucky Old Lady statue in Bravil. Her remains are removed from the crypt and brought to Skyrim after her tomb is desacrated by the Imperials. The Dark Brotherhood's beliefs say she is the wife of Sithis and bore five children, whose skeletal remains can be seen in her tomb.
The Night Mother's identity is shrouded in mystery as she is only met face-to-face under exceptional circumstances, appearing in a phantom-like form. She was first thought/suspected by many to be the daedric prince Mephala but later records indicate she was once a Dunmer and former member of the Thieves Guild who killed her own children, sending to thier father, Sithis.
She recieves prayers from those wishing to arrange an assassination and tells the listener who then pass's it on to the speakers who assign the quests to the Dark Brotherhood members. Clients wishing to contact the Dark Brotherhood would perform the Night Mother Ritual or Black Sacrament. The Black Sacrament involves an effigy of the intended victim -- created from actual body parts, including a heart, skull, bones and flesh -- within a circle of candles. To proceed with the ritual, one must stab the effigy repeatedly with a dagger rubbed with the petals of a Nightshade plant, while whispering the plea: "Sweet Mother, sweet Mother, send your child unto me, for the sins of the unworthy must be baptized in blood and fear."