Plutonius

Plutonius is a nuclear warhead worshiped as a god by a cult of ghouls in Kansas City

Background
It was produced by Manhattan Projects Inc.. Before the Great War, Kansas City was a major nuclear launch site. After the city was hit by the bombs, the surviving silo staff were turned into ghouls, and formed a town called Gravestone in the ruins of the city.

Only one nuclear bomb was left intact in the silos, and the ghouls took to worshiping it as a god, "Plutonius." Plutonius was later taken by the Brotherhood of Steel, placed on their nuke carrier, and used to crack open the entrance to Vault 0 in order to assault the Calculator.

Behind the scenes
The bomb's name is derived from the radioactive element Plutonium, one of the three primary isotopes utilized in nuclear fission.