At the tender age of ten, Fatman built his first nuclear bomb from scratch, thus earning his codename after the atom bomb dropped on Nagasaki during WWII. This feat impressed the Navy so much that they immediately recruited him to study under the tutelage of Peter Stillman, the world's foremost explosives expert. However, he would only work with Stillman as long as he believed he could learn anything useful, for Fatman had an obsessive need to surpass his mentor and be known as the best in his field. He quit soon after and embarked on a colorful freelance career until finally joining up with Dead Cell, rigging Big Shell with enough explosives to blow the entire facility sky high.
Fatman is notoriously unstable and unpredictable. He possesses a nihilistic sensibility and must be dealt with at all times using the utmost caution.
Little Boy and Fatman came to Gotham City to start business, but they are stolen by Angel Lupo.