The Raiders of the Lost Vault are a sadistic group of raiders who come from Vault 75 that was nearly destroyed in the early moments of the war. The vault was accidentally pumped with radiation causing the fusion reactor to overload which filled the vault with a type of gamma radiation mixed with nuclear radiation. This caused all the residents to become a mutated version of ghouls. This mutated version of ghouls were immune to radiation but still kept a human-like appearance, but with blood red skin.
They came across a small town called Scorge, and approached a merchant selling items. The merchant refused to talk to them, calling them 'red freaks'. The town sheriff asked them to leave, the vault dwellers refused, the sheriff shot one of the vault dwellers in the knee. In response the former vault overseer disintegrated the prejudice merchant. This caused a large scale firefight between the better armed vault dwellers, and the more numerous city men. The vault dwellers prevailed, realizing how hostile the wasteland is, began raiding towns and cities. They became known as Raiders of the Lost Vault.