Raktabij was a demon who fought with Shumbha and Nishumbh against Durga or kali. Raktabij was given a boon that even if one drop of his blood falls on the ground a duplicate Raktbij will be born. It is one of the best boons that any body could ever get.
However Goddess Kali was smarter than him and just swallowed every drop of his blood even before it touched the ground.
