fe·ral [fi(ə)rəl] adj. - (esp. of an animal) In a wild state, esp. after escape from captivity or domestication: "a feral cat".
Synonyms: ferine, savage
Etymology: c.1600, from Middle French feral "wild," from Latin fera, in phrase fera bestia "wild animal," from ferus "wild" (see fierce).
Or, if you're playing Fallout 3, this could be a person who was ghoulified by radiation.