Black Dahlia is a ruthless assassin and the killer of the Fishbone Gang. She sliced up Ms. Fortune and left her to die. She is also seen during Peacock's story mode protecting the head of the Medici mafia, Lorenzo Medici. At least one of her legs is robotic, and her right arm has also been replaced with a giant gun-arm. She's been in the killing business for decades, but beyond that, not much else is known about her. It is suspected that she is quite old, hinted at by her love of doilies.
While B. Dahlia was revealed to be one of the characters that fans could vote on to become a new DLC character, ultimately she was beat out by other characters. For the record, Black Dahlia made it through the first round of voting, but was eliminated in the second.