The characters from the French edition include (with names from the English translation in square brackets):
Nicolas (the main character) [Nicholas]: He is sensitive and attached to true values like friendship, love of one's parents, and has some sense of justice. He is not good at arithmetic and smallest in his class.
Clotaire [Matthew]: "He's bottom of the class."
Alceste [Alec]: Nicolas' best friend, "he's fat and he eats all the time."
Eudes [Eddie]: "He's very strong and likes to punch our friends on the nose."
Geoffroy [Geoffrey]: "His dad is very rich and buys him everything he wants."
Agnan [Cuthbert]: "He is ranked first in the class and is the teacher's pet and therefore nobody likes him, but you can't hit him as often as you'd like, because he wears glasses."
Joachim [Jeremy]: He has a little brother.
Maixent [Max]: He runs very fast because of his long legs.
Rufus [Rufus]: "His father is a policeman, and he's got a cop's whistle."
Marie-Edwige [Mary-Jane]: "She's very nice."
Louisette [Louise]: The daughter of a friend of the mother of Nicolas; Nicolas decides he wants to marry her because she plays soccer well.
Rex [Rex]: A stray dog that Nicolas found; his real name is Kiki.
Other characters include Nicolas's parents, as well as teachers and administrators in the school. The teacher is hard-working and loves the children, although they usually drive her crazy. The superintendent, Mr. Dubon, is known as "le Bouillon" ("Old Spuds").