Stanley "Stan" Marsh is an 8 year old boy. He's the most sensitive of the four boys. Stan doesn't agree to following popular trends, despite once becoming a goth after breaking up with his girlfriend, Wendy! He's very best friends with Kyle and even claims that he would donate a kidney to him even "if it hurt a whole lot". Stan is the ultimate lover, he refuses to hunt, tried to save baby cows and even returned a goat to its rightful owners! In the early episodes of the show Stan's girlfriend was Wendy Testaburger, but Stan was often sick with nerves when he saw her and eventually she broke up with him. Stan is often embarassed by his parents (Randy Marsh and Sharon Kimble Marsh) and other adults throughout the town, and is always going against what his parents say or do. Due to his parents, he has probably never respected or trusted adults.

Kyle Broflovski is 8 years old and the youngest of all the boys. When angered or frustrated, Kyle has a tendency to clench his fists and growl or yell angrily. His character Jewish and also diabetic. He shows the highest moral standards of all the boys, he also has the best ideas and highest grades. He has a very protective mother (Sheila) and is prone to making a huge fuss whenever the tiniest little thing may upset her son. At one point, Kyle nearly died of kidney failure, much to Stan's upset and he ultimately saves him by tricking Cartman into donating one of his kidneys to Kyle (they are both blood type AB). Kyle has an adopted younger Canadian brother, Ike and a father, Gerald, who is a lawyer but who has serious gambling problems. Ike follows Kyle around and generally imitates his older brother whenever possible.

Eric Theodore Cartman (just named "Cartman" to his friends) is the eccentric one. Some may say he's at the point of being evil, he's against any race or group that he isn't a part of like Hippies and Jews (hence his slight rivalry with Kyle). He often manipulates others into getting him what he wants (which he's good at) even if it means death or destruction. At first the little 9 year old was just an immature brat but as South Park has progressed he's more aggressive and self-centered (and even has a "Nazi-like hatred". Cartman is obese but shows no self-conciouseness, however he has a constant phrase: "I'm not obese, I'm big boned!". Cartman has a mother, but his father and sister were only ever shown in the first ever episode. However, he does have a cat called Mr.Kitty who (even though called Mr) is a female.

Kenneth "Kenny" McCormick is a 9 year old Roman-Catholic. Most of the time, Kenny has his hood on so that only his eyes are visible, although on some occasions when he gets frightened, he'll pull his hood over his face tighter, underneath his hood he has messy blonde hair. Kenny speaks muffled so that it's hard to hear what he says which is purposly done, as his lines are often rude. Kenny claims that he is best friends with Cartman because he feels sorry for him, and he is also claimed to be the most heroic of the four, he once even tried to save the world by sacrificing himself. Kenny's parents (Stuart and Carol McCormick) are poor because Stuart is an alcoholic, therefore they often eat frozen waffles. Despite being the poorest, he was the first in South Park to have a PSP and a miniature battery powered car. Kenny is mostly fascinating for having survived his reccuring deaths!