This 3-meter (9 feet) long half-man-half-snake inhabits the more and regions of Gamma World, often settling near an oasis or well. All Hissers are telepathic, with a mental strength of 12 and mass mind, sonic attack ability, and one other (random) mental mutation. Their scaly skin is completely resistant to laser and sonic attacks. Their society is matriarchal, one female leading a group of 70 or so males and young. She, like a queen bee, lays all the eggs for each settlement, and all of them hatch as males. When a community grows to about 70 individuals, the matriarch will hatch another female. In a few years, the colony will divide and the new matriarch will lead an assortment of male Hissers off to find a new place to live. Although intelligent, Hissers do not have any written or spoken language, as all information is exchanged telepathically. They utilize selected items of Ancient technology which they uncover in search expeditions among the ruins of the Ancients.

Hisser Matriarchs are like a male Hissers, but with planar travel.