Aunt Beast: Aunt Beast is one of the creatures the children encounter on the planet Ixchel. It is gray in color, walks upright and has four arms. Each arm has five long waving tentacles. It has a head and a face, but no eyes. However, the lack of eyes does not stop Aunt Beast from knowing and understanding things deeply. Aunt Beast is a benevolent, loving creature who helps Meg to recover after she has been paralyzed.
The Man with Red Eyes The Man with Red Eyes is the man the children encounter on Camazotz. He tries to hypnotize and brainwash them by posing as their friend. Calvin and Meg resist him, but Charles is overconfident and falls under the man's spell.
IT: IT is the disembodied, living brain that controls all thought and action on Camazotz.
The Happy Medium: The Happy Medium is a woman on a distant planet in Oriel's belt. Through her crystal ball, she shows the children the earth, which is shrouded by the Dark Thing.
Charles Wallace Murry: Charles Wallace Murry is a precocious five-year-old boy, the youngest son of the Murrys. He has a command of language far beyond what might be expected of a boy his age, although because he did not begin to speak until he was four, most people think he is stupid. Charles Wallace has a gift of understanding things that fall outside of normal human experience. It is he who first befriends the three ladies, and he has an uncanny ability to know what others are thinking. He can even understand the wind talking to the trees. Charles has a little too much pride, however, and it is this that makes him even more vulnerable on Camazotz than Calvin or Meg. As a result, he is taken over by IT and only freed by Meg's love.
Dennys and Sandy Murry: Dennys and Sandy Murry are the ten-year-old twin sons of Mr. and Mrs. Murry.
: Meg Murry is the twelve-year-old heroine of the story. Unlike her beautiful mother, Meg is plain. She wears glasses and has braces on her teeth, and she thinks she is unattractive. She also regards herself as an oddball. She does poorly in school even though she is good at math and science. But she solves math problems in her own way rather than the way she is taught at school. Meg can be stubborn, impatient and angry, but these qualities come in useful when she has to resist IT. Meg also loves her brother Charles Wallace dearly, and it is this quality that enable her to win him away from IT. During the course of the novel, Meg learns that her individuality is an asset rather than a liability, and she also learns that she must take responsibility for saving Charles herself, rather than waiting around for others to do it.
: Mr. Murry is a physicist with the Institute for Higher Learning in Princeton, who was working for the government on a top secret project when he disappeared. It turns out that he has been imprisoned on Camazotz by IT. He did not intend to go to Camazotz; his intended destination was Mars. The mistake happened because the science of tessering was still in its infant stages.
: Mrs. Murry, like her husband, is a scientist. She holds doctoral degrees in biology and bacteriology. She is a beautiful woman with flaming red hair, in contrast to Meg's plainness. She raises her children with love, common sense and tolerance, and she greatly misses her husband when he disappears.
: Calvin O'Keefe is a tall and skinny fourteen-year-old boy who meets Meg and Charles Wallace on the way to the haunted house. In contrast to Meg, Calvin is smart and very popular at school, being good at basketball and other sports. However, Meg is better at math than he is. Calvin enjoys the loving Murry family, which is such a contrast to his own. He accompanies Meg and Charles on their adventures, and develops affection for Meg and tries to protect her.
: Mrs. Whatsit is the first of the three old ladies that the Murry children meet. She is dressed rather like tramp. Later, on the planet Uriel, Mrs. Whatsit takes on another form, appearing as a beautiful creature with the lower parts resembling a horse but a torso, arms and head like a man. Of the three ladies, it is Mrs. Whatsit who is the best at explaining things to the children, and also the best at materializing. She is over two billion years old, but she is the youngest of the three.
: Mrs. Which is the last of the three ladies that the children meet. She never fully materializes because it tires her too much to do so. Mrs. Which is in charge of tessering, and it is she who tells Meg, as she leaves her on Camazotz in the final chapter, that Meg has something IT does not.
: Mrs. Who is the second of the three ladies that the children meet. She has a habit of talking by using quotations from famous writers because she finds it hard to verbalize her own thoughts.