On the surface, Reese is a notorious school bully and a mischievous trickster. He frequently targets kids weaker than him, and his favorite hobby is tormenting his youngest brother, Dewey. Often considered the least academic of the brothers, he severely lacks both book smarts and common sense, acting primarily on pure instinct. He is the oldest of his brothers Malcolm, who is one year younger than him, and Dewey, who is 7 years younger than him, and then the oldest sibling, Francis, who lives somewhere farther away living his own life, being 3 years older than Reese. Despite his foolish exterior, Reese is shockingly intelligent when it comes to mischief, manipulation, and intricate planning. Many of Reese's outbursts and violent tendencies are born from a desperate desire for love, acceptance, and attention. He has spiked hair with frosted tips, and his wardrobe matched his rugged, high-energy lifestyle. He was typically seen in casual teenager wear of the era: graphic T-shirts, baggy jeans, sneakers, and unbuttoned overshirts. Because Reese is constantly working out to maintain his dominance, he is generally depicted as lean, average height (5’8), and only very slightly muscular, despite the fact hes awful at fignting and such, distinguishing him from his more bookish brother, Malcolm. His demeanor was frequently characterized by an intense or goofy stare, reflecting his reckless nature, sudden panic attacks, or overconfidence.

His high IQ and photographic memory allow him to solve complex problems effortlessly. He views his intellect as a burden rather than a gift because it causes him to overthink trivial situations and isolates him from peers. Raised in a dysfunctional environment, Malcolm is highly critical of the world and his family. He often complains that life is unfair and has a hard time fitting in with average students or his own eccentric brothers. Malcolm is aware of his own intelligence, which frequently leads to condescending behavior and a stubborn need to be right. Despite his academic focus, he still participates in pranks and often bends rules to challenge authority figures. He acts as a "chaotic teen genius" who frequently clashes with school rivals like his teacher, Mr. Herkabe. his hair is a short, dark brown, spiky style. He is visibly shorter than Reese. He typically wears roomy Baseball Tees, striped sweaters, and baggy graphic t-shirts.

Dewey possesses a savant-level understanding of music. He teaches himself to play the piano expertly, directs a children's choir (the "Buseys"), and even writes an entire opera, often building crude instruments out of scavenged household items. He frequently outsmarts his older brothers Reese and Malcolm using subtle manipulation. Despite the family's madness, Dewey maintains a deep compassion. He is often the most emotionally observant of the brothers, frequently noticing things his family overlooks and acting as the moral compass of the house.

Lois believes in strict rules, unquestioning obedience, and harsh consequences. She struggles with anything out of her jurisdiction and constantly needs to manage the lives of her husband and children. She is notorious for her severe temper. Often pushed to her absolute limit by the daily stress of her chaotic environment, she is quick to use yelling, physical intimidation, and guilt-tripping to establish order. Despite her flaws, she is the primary anchor of the Wilkerson family. She is fiercely protective of her kids, deeply committed to her husband Hal, and willing to go to extreme lengths to make sure they survive their own misbehavior.

Hal is often more immature than his own sons. He is easily distracted, prone to intense but short-lived obsessions (such as roller-skating, race-walking, and painting), and lacks the authoritative composure typical of most sitcom fathers. He is madly and unconditionally in love with Lois. He views her as his "special treasure," defers to her judgment, and seeks her approval above almost all else. Hal is terrified of making the wrong choices, which often paralyzes him when forced to make tough family or ethical calls. Because of this, he avoids discipline and leaves the strict parenting to Lois, though he understands his boys' struggles and often acts as the fun, lenient parent.

He often serves as the intellectual equal and grounding force for Malcolm, using his trademark sarcasm and wit to point out when Malcolm’s ego is getting the better of him. Because of his overprotective parents, Stevie constantly pushes back against being treated like a "bubble boy," eager to prove his autonomy. Despite his severe asthma, speech impediment, and physical condition, he doesn’t back down—he even plays wheelchair basketball and occasionally stands up to the school's bullies.

Abe adores his son Stevie and takes immense pride in all his accomplishments. Following the departure of his ex-wife Kitty, he stepped up to comfort and guide Stevie, often shielding him while simultaneously encouraging his independence. He is generally upbeat, loves to lend an ear, and provides thoughtful advice.

After striking up a friendship with Lois, she tries to stand up for herself. This backfires when she goes completely mad, taking out her repressed anger aggressively on everyone around her.