Marvel Legends -- Black Cat

 

Black Cat was originally imagined as a villain for Spider-Woman, but when the writer who was creating her moved from Spider-Woman to Amazing Spider-Man, he brought the character with him. She eventually developed a relationship with Spider-Man similar to that which Cat-Woman shares with Batman. Eventually, they entered a serious relationship, as Peter Parker felt he could be open with her about his identity as Spiderman.

Eventually she gained powers which caused those around her to suffer bad luck. Eventually those changed to give her heightened strength, agility, etc.