A born troublemaker and proud of it, Reese isn't afraid to do whatever springs to mind at the drop of a hat regardless of how a bad idea it is, something which he acredits to the crazy voice he and all his brothers share. He's gotten into more trouble than either Dewey or Malcolm and was the biggest bully during middle school, something which the students were actually gradful for since him being a bully stopped an uprising of a hundred others trying to take his place.
Though his grades don't show it Reese is just as much a genius as his two younger brother's. Purposely getting a perfect zero on every one of his final school exam's, a feat which is just as difficult to acomplish as a perfect one hundred. He has also proven to be a very skilled cook, shown when he prepares thanksgiving dinner for the entire family.
In the series finale he has become the head janitor for his old high school, after the old one was fired after the school found peepholes in the girls shower. As soon as he got the job he left home on his mothers demands and now lives with Craig.
Reese, played by Justin Berfield, is the second oldest of the children, and also appears to be the least intelligent and most destructive, although at some times, he shows even more intelligence than Malcolm when devising fiendish plans. He also has scored high on tests, when he set his mind to it, and had nothing to do but study, as shown in the episode in which he is kicked out and is alone, in which he is referred to as the "most improved student ever seen" by his teacher. Reese is often too tied up in violence and laziness to try to learn, and appears to have immense problems focusing. He even had a mean streak in the womb; while Lois was in labor, he kicked her so hard that she delivered him prematurely. Immediately following his delivery he kicked the doctor in the nose. His obsession with violence horrifies the family and leaves him with few friends, partly as he is a bully at school. He bullies the "Krelboynes" in Malcolm's class, (except Stevie who, because of being paraplegic, is "off limits" except in certain situations), as well as his younger brothers, especially Dewey. Reese is often seen exercising, to build his muscles.
During his teen years, Reese ran off to join the US military under a faked name and forged age (he was underage at the time) without telling his family where he had gone. He was successful in completing Basic Training and was praised as one of the most brilliant soldiers in his platoon after he learned to "turn his brain off" and surrender his will to his superiors. After being sent to Afghanistan in combat conditions, Reese struggles to stay alive and in the process winds up unwillingly marrying an Arab man. When his mother, Lois, catches wind of what Reese has done, she tracks him down in Afghanistan and personally brings him home without objection from the military since Reese was now found to be underage.
Despite Reese's outwardly unintelligent facade, he discovered a gift for cooking in his early teen years. He is gifted at gourmet cooking and enjoys it; the only effective way his parents can find to punish him is banning him from the kitchen. He finds success in a meat-packing job, but is fired after setting all the cows free (trying to impress a girl).
In his late teen years, Reese marries an attractive immigrant girl who requires the marriage to stay in the U.S. Reese truly cares for her, and she claims to care about him, despite her dominating personality and refusal to have sex. However, the marriage falls apart when Reese and Lois discover her sleeping with another man inside the couple's "garage apartment" (they lived in his own parents' garage). Added to the fact that Reese miserably failed the immigration test to keep his wife in the country (he mistakenly wrote that she has a tail), the character is never heard from again and presumably deported.
Reese is depicted as a virgin with limited sexual experience. In the penultimate episode, "Morp", a girl named Jeanie offers to pay Reese to take her to the senior prom because she had been too focused on getting into college to cultivate a social life and find a date by normal means. Jeanie says that she initially selected Reese because he is not "completely hideous" and she knew he would not have a date. However, Reese turns out to be a gentleman and sweeps her off her feet by being charming and considerate. Although Jeanie did not initially plan to do anything with Reese after the prom itself, she invites him to go to the beach with her and tells him, "I really want you." However, before Reese can accept the invitation, his watch alarm goes off, indicating that he is "off the clock", and he leaves, revealing that he was only nice to "satisfy his customer" and thereby passing up a chance to finally have sex.
After graduating high school, Reese moves in with Craig Feldspar and finds success as a janitor in his former high school. In a telephone conversation with Malcolm in the season finale, Reese says that when the principal found the peepholes in the bathroom, the head janitor was fired, and his job was given to Reese.