Beast was born on May 22, 1864, without a left leg, as Mally to a scullery maid named Amelia. She grew up in an alley in the East End, referred to as a gutter, with the other first-string circus members. Joker stated that they came together because they were each defective in a way. In Beast's case, she has been missing her left leg since birth.


Ten years ago, Doll rushed up to Joker one day with a tooth in her hand. She gleefully exclaimed that it fell out and promised she would buy them all bread later, believing that she would later get a coin from the Tooth Fairy. However, she was oblivious to the fact that it did not actually exist. Beast commented that if Doll did not get her coin next morning, she would be extremely upset, to which Joker decided that he should attempt to earn something. Beast, Joker, Dagger, Peter, Wendy and Jumbo then proceeded to work on manual chores earnestly all night long in order to earn a single coin for Doll. They were relieved to see they made it on time as they placed it beside her whilst she was sleeping. The next morning, an oblivious Doll showed off her coin to them, stating how happy she was that they could eat bread with it and an exhausted but happy Beast smiled along with her. However, in the belief that the Tooth Fairy would give her more coins, Doll later attempted to take out more teeth that weren't wobbly, to the dismay of the others.


As thieves, they were unsuccessful, and they barely managed to survive. At some point, Baron Kelvin found them in the alley and adopted them. While there, Beast seemed to have developed her crush on Joker, as she was touched by his offer to carry her on his back if he still had both arms, and was very glad to be in his presence.


After living at Baron Kelvin's manor for some time, they decided to start a circus, and Joker gave her the stage name "Beast," which, initially, she was not excited about.