Terrance Mephesto
| Gender | Male |
| Age | 10 |
| Hair Color | Dark Brown |
| Occupation | Student |
| Grade | 4th Grade |
| Religion | Roman Catholic |
| Father | Alphone Mephesto |
| Mother | Unknown |
| Brother (adopted) | Kevin Mephesto |
| Voiced by | Matt Stone |
| First Appearance | An Elephant Makes Love to a Pig |
Terrance was a rival of the boys who participated against them in the South Park Elementary Science Fair early in the third grade, working with Bill Allen and Fosse McDonald to clone a human. He and his father successfully engineered a human foot and later Evil Clone Stan who rampaged across the town. Since their failed attempt against the boys, Terrance has receded to the background.