In "Destroy All Humans!", players assume the role of Cryptosporidium 137 (Crypto for short), a warrior and member of the Furons, a race of war-like extraterrestrials with a large empire constantly seizing new worlds through conquest. After centuries of warfare against inferior species using unchecked nuclear weaponry left their species impotent and without genitalia, the Furons were unable to sexually reproduce and became forced to turn to cloning as a means of reproduction, as well as a process by which to achieve immortality. However, after generations of clones, the Furon DNA is degrading, and each clone is becoming less and less stable.