Rudy Tabootie (voiced by E. G. Daily) is a 10-year-old fifth-grader who loves to draw, but Reggie Bullnerd (Candi Milo), the school bully, is always teasing him or getting him into trouble with Mr. Wilter (Robert Cait), Rudy's grumpy school teacher who strongly dislikes cartoons. One day Rudy discovers a piece of "White Lightning" chalk, which allows access to the ChalkZone, a place where everything and everyone that has ever been drawn in chalk and erased takes form as living or is tangible. He soon makes friends with Snap (Candi Milo), a small, blue, humanoid drawing made by Rudy when he was only eight. Snap wears a superhero uniform and is very adventurous and witty. Rudy only lets one other person know about ChalkZone, his best friend and crush Penny Sanchez (speaking voice, Hynden Walch; singing voice, Robbyn Kirmsse), who acts as the genius of the group.
While in ChalkZone, the trio are introduced to Cyclops (Rodger Bumpass), the kilt-wearing guardian of the magic chalk mines where Rudy obtains his magic chalk (Rudy later draws a second eye for him and renames him "Biclops"); Queen Rapsheeba (Rosslynn Taylor), ChalkZone's song artist whom Snap has a crush on; and Blocky (Candi Milo; Robert Cait), a light green block friend of Snap's and Rudy's first-ever drawing. They are also faced with villains such as Skrawl (Jim Cummings), a drawing who blames Rudy for being ugly and wants to destroy him; and the Craniacs (Rob Paulsen), a series of robot drawings obsessed with collecting futuristic devices.