A young Maori woman living in Melbourne, Australia, the woman dubbed the Human Block was once inexplicably struck by lightning and survived the incident. Unknown to her, this similar event had happened to many other individuals throughout time, and was in fact the speed force imbuing her with speed related abilities. In -her then present time - 1957, Block acted as a side show attraction in a carnival. The prize of $1000 going to whoever could move her which was failed by many as she had manipulated her body density. One drunken man staggered onto the stage to accept her challenge, making her move by insulting her Maori heritage rather than physically moving her. Angered she immediately struck out at him and instigated a small brawl, tearing through the crowd before someone hastily drew their firearm on her and shot, only to find that not even bullets affected her. Before the now turned mob could attack her, Zoom accompanied by his newly recruited acolytes Folded Man and Magali appeared and teleported her outside of the carnival grounds. Being offered the chance to embrace her abilities and live as a godlike being after mastering them, she did not hesitate to join Zoom and his quest to kill the "evil" Flash.
Along with the other Acolytes, she would train for what would be an unknown amount of time to kill the Flash, facing off with Zoom in his place. It's unknown how long this training took place as they stated that over the course of centuries this team trained to take on the Flash, and when they reached older age Magali would revert them back to their original ages when joining.
Unknown to Block, Zoom is actually the one to have orchestrated her joining him to begin with, appearing to the drunk man who challenged her while convincing him that the way to make her move was to attack her heritage, as he had been keeping close watch on her for some time.
Being imbued with the speed force, Block has the unique ability to slow down her atoms. In doing this, they become denser than steel and grant her invulnerability, super strength, and immobility. She can possibly slow down other speedsters if not other people as well through physical touch, as she stopped the Top's ability and was able to hold Zoom in place in a headlock. After training centuries with Zoom, she is a deadly fighter. Recently she was able to stop the molecules around herself to make the air unbreakable.