The various types of mutant creatures that inhabit the Wastelands were mostly created by radiation. This is where mantises, geckos, radscorpions, brahmin and the various mutant rodent species originated from. Radiation is also how ghouls - decrepit, zombie-like victims of massive radiation poisoning - are created. Many ghouls were once Vault dwellers living in Vault 12 under the city of Bakersfield (better known as the Necropolis after the War). As part of the vast Vault Experiment Program, the Vault 12 door was designed not to close properly. Thus, the vault's inhabitants were exposed to massive amounts of radiation, leading to most of them becoming ghouls.