Alllright. The Black Lady was the result of Chibi Usa's exposure to the dark power of the Wise Man. The Wise Man tricked
Chibi Usa into thinking that she was totally unloved. He altered her memories and so
Chibi Usa was filled with anger and hatred. She absorbed the dark power and turned into an older version of herself, becoming The Black Lady.
The name is also referred to as Wicked Lady.
The Black Lady was determined to destroy everything and everyone because she was angry at the world for not loving her. She was the most powerful of The Wise Man's minions, and had no mercy. The Black Lady used Luna P in combination with the dark power for a variety of powerful attacks.
She killed Saffiru. ;__;
The Black Lady eventually realized that she is loved (By help of the senshi..) and reverted back to being Chibi Usa, who helped Sailor Moon defeat The Wise Man in the