Characters
Malcolm (played by Frankie Muniz) is the title character of the series. Malcolm is a genius with an IQ of 165 and a photographic memory. He is placed in a class for gifted students (or "Krelboynes" as they are known at the school). His high intelligence, as well as feelings of not fitting in, and a large ego fueled by a cruel streak of snarkiness cause numerous problems for him over the course of the series. As the title suggests, Malcolm is initially the middle child of the three living at home; chronologically, he is Hal and Lois' middle son. Despite his intelligence, Malcolm is just as immature and destructive as his brothers and is often the ringleader in their schemes. Throughout the show, Malcolm often strives for independence away from his controlling mother and often tries to have her see him as an equal. Due to his intelligence, Lois often makes decisions that she feels will benefit his education while keeping a close eye on him. It is revealed in the series finale that she does this so that he will one day become the President of the United States and use his position to help lower-class families like their own. His best friend is Stevie Kenarban. In the series finale, he graduates from high school and starts attending Harvard University by both scholarship and working various jobs, specifically as a janitor.
Lois (played by Jane Kaczmarek) is the family's temperamental and overbearing mother who is also an intelligent and decisive woman. Most of her bullishness comes from her constant battles throughout the series to keep her badly behaved, highly destructive boys in check, while maintaining a menial job at a Lucky Aide drugstore, as well as her own difficult upbringing with a tyrannical mother and an indifferent father. Though she is hard on her children for their constantly bad behavior, Lois can be just as petty and spiteful as them, e.g., going after a group of girls that humiliated Reese before his senior prom. Despite her constant aggressiveness, she is motherly and will defend her family fiercely, especially against neighbors and others who view them as poor trash; in one episode, she finds that Malcolm and Reese discovered their neighbor having an affair with her Mexican gardener while they planned to frame her son for theft, but does not punish them for their actions as this counted as revenge against the woman, who despised Lois. Lois is disliked by both Hal's wealthy family and her own parents. She has a younger sister named Susan, who blames Lois for stealing Hal from her. Neighbors hate Lois and her sons and celebrate the weekends when they are gone. In the series finale, she discovered that she and Hal are expecting a sixth child.
Hal (played by Bryan Cranston) is Lois' husband and father to Francis, Reese, Malcolm, Dewey and Jamie. Hal is a well-meaning, loving, but inept and completely immature father, and completely dependent on Lois, whom he loves absolutely. He comes from a wealthy family that does not accept Lois as his wife and who wish that he had married Susan instead. Because his family is disrespectful towards Lois, he rarely mentions them and avoids his family. Hal loves his boys and will sometimes sneak them out for fun father–son activities behind Lois' back. Hal is an indecisive character who frequently picks up new hobbies for short periods of time, such as speed walking or painting, and is irresponsible with the money he earns from his office job. His indecisiveness was explored in "Living Will" from a childhood which he had a hard time making decisions for himself and because of this, he always deferred to Lois to make them for him. In the series finale, he discovers that he and Lois are expecting a sixth child. Hal has a high sex drive, as revealed in the episode "Forbidden Girlfriend", and it is mentioned in the episode "Poker 2" that he has sex 14 times per week. Hal's best friend is Abe Kenarban.
Francis (played by Christopher Kennedy Masterson) is Hal and Lois' oldest son. At the beginning of the series, he is attending military school in Alabama, run by the strict Commandant Spangler (Daniel von Bargen). It is shown that his parents enjoyed a promising middle-class, comfortable lifestyle before he was born and that he was such a difficult, destructive child that their dream soon ended. He has himself legally emancipated at the start of season three, leaves the school, and travels to Alaska. He finds work at a logging camp and later meets and marries Piama (Emy Coligado), a girl of Inuit heritage. When the camp closes, they move to the western United States and take jobs at a Wild West–themed hotel/ranch, run by kindly but eccentric Germans: Otto Mannkusser (played by Kenneth Mars) and his wife, Gretchen (played by Meagen Fay). Francis and his mother have a mutual love–hate war of wills, and his main motivation in life is to thwart or irk her (though, ironically, he marries a woman with the same personality as Lois). Although a juvenile delinquent, he is streetwise. Francis is seen less frequently after season five, becoming a recurring character and making only a small handful of appearances in season six and season seven, which is the show's final season. Francis' steady job disappears in season six due to legal issues until the series' finale, "Graduation", reveals that he has been working for a few months in a stable tech company job entering data into computers. He admits to Hal that he likes his job, but also enjoys frustrating Lois by lying to her that he's unemployed.
Reese (played by Justin Berfield) is Hal and Lois' second son. The older brother of Malcolm, Dewey and Jamie, and younger brother of Francis, Reese is the most impulsive and physical of the boys. Lacking common sense, he is frequently outwitted and outspoken by other family members, and is gleefully violent. Despite being dimwitted, Reese is able to devise plans thoroughly (although most of his plans tend to backfire), and is masterful at the rare tasks which can pin his drifting focus, such as driving, or cooking and baking (he is revealed to be a culinary prodigy). In the series finale, he finally graduates from high school after intentionally failing many times before, obtains full employment as a high school custodian, and shares an apartment with Craig.
Dewey (played by Erik Per Sullivan) is Hal and Lois' fourth son. He is the youngest child until the birth of Jamie, and often falls victim to his brothers' pranks. Starting in season 4, Dewey is shown to be very intelligent and musically gifted as he begins teaching himself to play the piano. He has a very high tolerance for pain due to years of physical and mental abuse from his brothers. Dewey often resorts to Machiavellian schemes to one-up his brothers and parents. Despite his intelligence, he is placed in a remedial class for slower students (or "Buseys") due to a misunderstanding. Dewey remains in the class and serves as their self-appointed teacher. By the seventh and final season of the show, the Busey class is no longer mentioned. He is the only sibling that eventually breaks the cycle of abusing the younger sibling, which ends up with him acting like a normal, lovable brother towards Jamie. In the series finale, he and Jamie are last seen hiding in the closet together after a prank, continuing their older brothers' tradition of incurring Lois' wrath.
Caroline Miller (played by Catherine Lloyd Burns) is Malcolm's teacher (seasons 1–2).