Developed by Kirk Langstrom using the DNA of bats, this serum was intended to help the doctor find a cure for his worsening hearing loss.
However, while it did improve his hearing dramatically, it also led to Kirk becoming a giant man-bat hybrid.
Man-Bat and Langstrom were two separate entities sharing the one body, each with their own desires and impulses.
Although Langstrom was able to create several cures for the serum, allowing him to control his transformations, the results of the initial serum were permanent.
Talia al Ghul and the League of Assassins kidnapped Kirk's wife, Francine, forcing him to manufacture and mass-produce new and more potent variants of the serum. If he refused, she would die.
