Vault 75 was programmed to slowly place radiation in the vault's air system over many years in an attempt to make humans immune to the effects that radiation causes. Unfortunately, the air system malfunctioned, causing it to release near lethal levels of radiation. This caused the vault's reactor to overheat, and explode; releasing a different kind of radiation. Most of the vault's residents died during the chaos, but 77 survived. These survivors had an odd mutation, blood-red skin. They left the vault in attempt to find another shelter, donning weapons from the vault's armory and wearing vault security armor.
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 prejudiced merchant. This caused a large scale firefight between the better armed vault dwellers, and the more numerous city men. The vault dwellers prevailed. After realizing how hostile the wasteland is, they began raiding towns and cities. They became known as Raiders of the Lost Vault.