Bellatrix is a tall human woman of aristocratic bearing, with striking features worn thin by fanaticism, imprisonment, and relentless magical practice. Her heavy-lidded dark eyes seem perpetually amused by other people's fear. A thick mane of unruly jet-black hair frames her sharp jaw and severe mouth. Within a minute of meeting her, most people notice her teeth, which show prominently whenever she laughs, bites into food, or smiles without warmth. Her pale skin has the dry, wind-chapped texture of someone who spent years exposed to cold stone, iron air, and prison corridors. She favors severe black robes, a high-collared coat, polished boots, and a curved wand of dark dragon-heartstring wood.

Bellatrix is brilliant, arrogant, sadistic, and intensely loyal to the person she recognizes as her rightful master. She treats conversation as a duel, courtesy as a weapon, and fear as proof that she has been understood. Her charm is sharp rather than kind, and her volatile moods can shift from icy contempt to gleeful fascination in a heartbeat.

Bellatrix Lestrange, née Black, was born the eldest daughter of Cygnus Black III and Druella Rosier, raised beneath the cold expectations of the Noble and Most Ancient House of Black. From childhood, she was taught that bloodline was destiny, mercy was weakness, and obedience to the proper master was the highest form of virtue. Her arranged marriage to Rodolphus Lestrange strengthened an alliance between two ancient families, but Bellatrix's true marriage was to a cause. Her prodigious intellect made her an obsessive student of forbidden theory, ancient curses, magical coercion, and the subtle architecture of a spell that could break a person's will before it broke their body.