Prior to moving into Grandyle, the Rats' history is mostly unknown. Some claim the group may date back to the opening of Vault 91, while some say it was only recently founded.
In 2259, a nameless group of nomads settled down in the Grandyle sewers. There were one or two other groups of raiders in the town at this time, and the group had to fortify a small building above the sewers to protect the little resources they had. Over time, they became accepted as a group of raiders themselves, taking on the name "Sewer Rats" due to their original base. Eventually, around 2263 or 2264, they forced the other groups from the area, taking a much larger chunk of the town for themselves. It was around this time they became firmly established on Grand Island as a serious group of raiders. It was around this time they first started to enslave and sell travelers, and found it to be quite lucrative.
By 2270, they were the only slaver group on Grand Island, and in control of most of Grandyle Village. It was in 2275 that Bennett Devereux first joined their ranks. Over the next few years, he moved up, and became the leader of the Sewer Rats in 2277, after having killed the previous one. Since then, the Rats haven't much ventured out of the village, aside from trading and such in Overpass.