She was a member of the House Of Black an old wizarding family and one of the Scared Twenty-Eight. Cassiopeia started her education at Hogwarts School of Witchcraft and Wizardry in 1973 and was Sorted into the Slytherin House.
Sence birth she was betrothed to Argus Bulstrode, who was apart of the last pure-blood branch of the Bulstrode family tree and married him two years after she graduated. She soon became a death eater to please her family and her husband but regretted it greatly afterwards.
in 1997, almost three months after her husbands death in the department of mysteries. She gave birth to a baby girl whom she named: Athanasia Druella Bulstrode.
Cassiopeia was born in 1962 to Cygnus Black III and Druella Black (née Rosier), who raised her to be proud of her Pure-Blood heritage. Although as she got older she didn't really care for blood purity but hid it in fear that she would end up like her sister, Andromeda, she also was a favourite to her younger cousin Regulus.
Cassiopeia came from the Pure-Blood Black family, therefore she was given a rich lifestyle. Cassiopeia attended Hogwarts School Of Witchcraft and Wizardry and was sorted into the Slytherin House. Her parents arranged her a marriage to Argus Bulstrode, a ruthless death eater and a pure-blood, slytherin. He was from the last pure-blood branch of the Bulstrode family.
First Wizarding War (1970-1981)
During the first wizarding war Cassiopeia had started and finished Hogwarts. However she was not a death eater then nor did she fight for Voldemort's side.
Between The Wars (1981-1995)
After Voldemort's fall. Cassiopeia married Argus Bulstrode. A Wealthy pure-blood and slytherin. It was him who manipulated her into joining the death eaters when Voldemort returned to power, saying that she would shame her family (Knowing that she had a constant fear of rejection). So she joined in July 1995. Cassiopeia despised Argus with passion. But remained quiet and submissive like a wife was expected to do. In a conversation with Narcissa she asks how her husband is and Cassiopeia responds with "Same as always, sleeps like the dead and sweats like a pig" which Narcissa responds with a awkward smile and looks away. This shows Cassiopeia's inner dislike for her husband and her more 'matured' personality.
The Second Wizarding War (1995-1998)
When it was said that Voldemort returned Cassiopeia was scared but happy because she could finally become a death eater. She became one in July 1995. At the meeting in the malfoy manor, Bellatrix realised that she wasn't as 'sensitive' then she was when they were younger.