Felicia Hardy, aka Black Cat, is an ally and a former enemy of Spider-Man. She is capable of giving people various forms of misfortune (e.g. making their guns faulty, causing them to trip and making their weapons misfire) at far range.
After a series of misadventures with Spider-Man and learning she can use her bad luck influence to fight crime, she became a valuable ally. She and Peter have dated at various points in time, though she has ultimately accepted his relationship with Mary Jane Watson.