Atom's Wrath was programmed by the Children of Atom to defend the members of the church's congregation in the Glowing Sea. It was on a mission with Brother Henri and his group to claim the Sentinel Site and the Mark 28 tactical nuclear warheads housed there for the cult. In their attempt to activate the launch sequence a nest of feral ghouls was disturbed and all but Atom's Wrath and Brother Henri were killed.
Atom's Wrath takes its lead directly from Henri, meaning it will remain passive as long as the Sole Survivor doesn't provoke Henri into resorting to violence. Should the mad cultist be turned hostile in any way, be it by mocking him in dialogue or by other means, Atom's Wrath as well as the nearby machine gun turret will join him in attacking the trespasser. Since said fight will most likely happen in extremely close quarters, the assaultron usually won't get much of a chance to deploy its devastating eye laser weapon, thus somewhat mitigating its threat potential. Its powerful melee attacks can still pose a minor problem for an unprepared player, mostly due to the robot lurking in an alcove from where it will spring a surprise flanking attack if the player didn't pay enough attention to their surroundings before engaging Henri in dialogue. On the other hand, everyone who made it this far into the Glowing Sea and the Sentinel Site is likely to be wearing power armor and packing enough firepower to not be bothered by a lone assaultron and its insane charge.