I would like to propose the following fan fiction origin for Atomic Man and Bullet Man.
Andromache was an advanced cyberneticist working for the AT at one time. His
prototype was a top secret AI/android project to assist in AT
expeditions. When Man-of-Action, Mike Power, was severely injured on a
mission, Andromache used his expertise to develop the Atomic Man
prosthetics to facilitate his recovery.
Mike's injuries were the
result of a first encounter with a budding terrorist organization,
COBRA. Because of this new threat, Andromache took it upon himself to
arm his prototype with cutting edge technology. That enhanced prototype
became... Bullet Man!
Andromache went missing sometime afterwards, and is presumed dead.