In addition to Scuzzlebutt, "Volcano" included the first appearances of recurring characters Randy Marsh and Ned Gerblanski. In this first appearance, Randy is identified only as the South Park geologist, and it is only in the episode "An Elephant Makes Love to a Pig" that he is first introduced as Stan's father. Parker, who provides the voice of Randy Marsh, said the design, voice, and personality of the character are based on his real-life father, who works as a geologist for the United States Geological Survey. Parker said his father is very calm in real life and Randy's relaxed reaction to learning of the volcano—calmly sipping his coffee—is "about how my dad would react to anything". The look of the Ned character was based on a drawing Parker made in high school, although the character did not originally have a voice box. The voice was inspired by a waitress who worked at a Kentucky Fried Chicken restaurant in Boulder, Colorado, where Parker and Stone would visit while attending the University of Colorado. The duo said they would go to the restaurant just to hear her voice, but that it was so low they would lose their appetite when she took their orders. Stone and Parker had trouble creating the right voice for the character; they tried putting the microphone directly on their throat, and also bought an actual voice box, but ultimately decided that the best way to provide the character's voice was with natural voice simulation.