In
Madeleine L'Engle's
A Wrinkle in Time series, Charles Wallace (who never, ever goes by Charlie, Chuck, or any other
nickname) is
Meg Murry's extraordinarily intelligent kid brother. The son of a biologist mother and a father who does secret work for the government, Charles Wallace is small, straightforward (though shy) and often picked on at school, by both
bullies and the
forces of darkness.
At one point, Meg must travel inside his body at a infitesimally microscopic level to fight the evil powers that wish to destroy him. Later on in the series, Charles Wallace appears in A Wind in the Door, as a central character along with Meg and Calvin O'Keefe, the next-door neighbor.