Board Thread:Lore Discussion/@comment-82.148.179.159-20130807135516/@comment-6881629-20130807144117

According to her wiki page basicly she was a member of the Thieves Guild but found it easier to just kill the victim, she left the Guilld and with some splinter members of the Morag Tong started what became the Dark Brotherhood. Depending what you read though she a Dunmer (the most likely) posably a Redguard or even Mephala.