- "I expect nothing and I'm still let down."
- ―Dewey at one of his birthdays
The eccentric child, Dewey is known for for his quirky behavior and slightly manipulative ways (e.g, Dewey often sticks things into his ears). Dewey is the 'baby' of the family for most of the series, coming an older brother when Jamie is born in the finale of season four. He is more artistically inclined than his brothers, playing piano and composing opera music in later episodes. In the first season, he was in the first grade.
Despite being the youngest at the time, Dewey was also the most poorly treated of the boys. All his birthdays have been horrible. Either his brothers beat him up on it or Lois and Hal forgot it completely. He is usually ignored, with his parents not even bothering to go to big events with him at center. As such, Dewey has no true problem scamming them with a smile on his face and seems to enjoy whatever misery he can personally cause them.
In earlier seasons, while a young child, Dewey was shown to have an extremely poor grasp of reality. Often from his point of view he asks Lois and Hal for something, while in reality he is throwing a horrendous tantrum. He also believed characters on TV were actually talking to him. Even his memories and fantasies stray from reality and the current situation greatly.
Dewey is also revealed to be almost as intelligent as Malcolm (probably even more so), however, he was put in the special needs class (also known as the "Buseys") because of an accident caused by Malcolm. Despite this, this doesn't conflict his performance, as in the beginning of season 6, he was almost put back to the mainstream class, until he threw a temper tantrum, not because he was angry but because he realized that the Buseys consider him their leader and without him to help them they would be much worse off.
Unlike his brother he displays a great deal more common sense, subtlety and is more emotionally grounded--he can trick both his brothers and parents into doing things easily but seems to play down his genius in order not to be forced into things as Malcolm is, he hid his intellect from his fellow brothers to the point that not even the viewers knew he was a genius until his intellect started to sprout during season 4, this was supported when he was shown to have built his own homemade organ out of many tools which drove Hal to insanity, thinking someone was stealing from him, Dewey built the piano solely because Hal wouldn't buy him one, though he was shown to have obtained his own custom made electric piano after this proving he is capable of owning one, like Reese has a talent for cooking, Dewey has a talent for music and was capable of making his own opera though he is also shown to have a talent for magic even performing his own magic show in front of a shopping mall.
He is the main victim in many of Reese and Malcolm's pranks, and as a result has an apparent hatred for Reese and is satisfied with any misfortune he suffers and has personally tortured him on numerous occasions and enjoys every minute of it. Although, in season 7, Dewey and Reese are close friends. While Malcolm enjoys torturing Dewey as well, the two seems to work together well on a few occasions such as pranking Reese, though Dewey still enjoys it when he is able to take revenge against Malcolm for his harsh treatment.
Ironically, despite being the youngest child for most of the show, he is often neglected by his family and receives the least amount of attention from his parents, because of this, Dewey does everything he can to make sure Jamie isn't neglected like the way he is even going far as to force his parents into a scavenger hunt and find party supplies for a party that was for Jamie while they thought it was for him, for each supply found Hal would receive a piece of his wallet which was held hostage by Dewey, Hal gave this wallet to Dewey in a blind rush to get him out of the house so he and Lois could have sex, it was revealed that Dewey spent hundreds of dollars on Hal's credit card for the party mainly because because he had to keep a Chucky E Cheese open after hours, Lois in the end mentions that even though she was still going to punish him, it was still a good thing he did for Jamie, this is not present in the earlier seasons possibly because the show was still developing.
Because he was young, Dewey was shown to eat almost anything that catches his eyes like toy heads, teddy bear eyes, marbles, and even underwear.
Unlike Malcolm, his family expect Dewey to lead a happy and fulfilling life.
Dewey's final scene in the series shows him and Jamie hiding from their parents after they pulled a horrible prank and Dewey realizes he and Jamie now have a shared secret to keep them bonded as brothers, just like Dewey had with his other two brothers before they destroyed the evidence when they moved out (the nuclear option).
Dewey, while being highly detached from reality, can be stoic at times. For example, when Malcolm and Dewey were trapped in a tiger pen, he assured his brother calmly that they would be okay.
He is a very good big brother despite his less than stellar relationship with his family, making sure Jamie doesn't feel alone by always playing with him, and is generally shown to be a better brother to Jamie than his brothers were to him. Lois describes him as a 'flyer' who will drift into happiness. Dewey longs for more attention from his family, being often forgotten and ignored, despite this, it is hinted that he is the favorite in the family. Because he is often neglected, when someone promises him attention he will hold on to the promise giving him a history of holding grudges. despite being a genius like Malcolm, he is the exact opposite in terms of personality.
Dewey, unlike any of his older brothers understands that his mother can be a genuinely nice person if you don't get her mad. He was able to form a normal mother/son relationship with her for a short while by not doing anything wrong while Reese and Malcolm are unable to perceive that their mom is anything but a sadistic witch who enjoys punishing them for no reason. In season six, episode 19, Dewey sells his electric keyboard to get himself a tattoo across his chest that says 'Lois is my mother' to prove his loyalty to her after 'cheating' with another mom. Lois screams that she is taking him to get get it removed immediately, though she is also very touched.
"Give Reese a slice from the fuzzy side and I didn't see a thing." ―Dewey to Lois after seeing her drop a roast on the floor.
Out of all of his brothers, Reese is the meanest to him and he is Dewey's archenemy. Reese has tortured and bullied Dewey from the minute Lois brought him home from the hospital and enjoys every minute of it. Dewey remembers every horrible thing Reese has ever done to him and always seeks to get revenge against him. It is very evident that Dewey sincerely enjoys any misfortune that Reese suffers and has personally tortured him on numerous occasions such as in "Reese Drives" and "Jessica Stay's Over" and enjoys every minute of it. Dewey has even gotten Reese physically beaten up as well. When Reese moves out in "Reese's Apartment", Dewey tries his hardest to make sure Reese does not return home and enjoys his absence. It is revealed that Reese also tortures Dewey by making him his personal slave. Despite their bitter relationship, Reese does not hate his younger brother and in "Ida's Boyfriend" felt genuine remorse for breaking Dewey's ship and attempted to get Dewey to stop ignoring his existence. Despite that Reese is mean to him more than Malcolm is, Dewey actually prefers Reese, as he is not a drag like Malcolm. The two have gotten along on numerous occasions and in "Hal's Christmas Gift", they get along very well when Malcolm is excluded from their activities.
Like Reese, Malcolm has bullied Dewey since he was an infant and enjoys making him miserable and is mean to him on numerous occasions. Dewey seems to dislike Malcolm somewhat and considers him to be an extremely annoying drag due to his massive ego as revealed in "Hal's Christmas Gift" where he and Reese have fun together while completely excluding Malcolm. Dewey enjoys any misfortune that Malcolm suffers and in "Dewey's Special Class", even after Malcolm tried hard to save Dewey from the special needs class told Lois that he sabotaged him and in all probability got him in serious trouble. Dewey has also on a few occasions outsmarted Malcolm and taken advantage of him. Despite their poor relationship, Dewey and Malcolm do work well together on a few occasions such as when they want to pull pranks on Reese and the two have gotten along on numerous occasions.
Due to their age difference, Francis did not seem to take part in Dewey's childhood torture and the two seem to have a decent brotherly relationship. In "Malcolm's Job", Dewey goes to Francis to finally have a nice brother and Francis is kind to him and Dewey tells him that he is the only nice person in the whole family. Francis however has ignored Dewey on a few occasions alongside the family and in "Blackout" threatened to hurt him if he told of his presence at the house. Francis has also taken advantage of Dewey as well, but despite this however, the two have a stable relationship. Francis is his favorite brother, and he is also Francis's favorite brother.
At first, Dewey did not seem thrilled that Jamie would replace him as the youngest son but the two have a good relationship. Dewey does not torture his younger brother in the same way that Reese and Malcolm torture him and tries to be a good brother. Dewey once even manipulated both Lois and Hal to give Jamie a proper birthday party and not neglect him the way they neglected Dewey. While Dewey does employ Jamie as his personal slave, he is not as forceful and mean as Reese is to him. In "Watching the baby' Dewey does however reveal that he will screw Jamie over in a heartbeat to escape punishment and on a few occasions, Jamie has gotten Dewey in trouble. Despite this however, the two have a good relationship.
- "You want to know the truth? You were the fourth child. By the time you came along, this house was in a state of complete chaos. The only sleep I got was when I'd nod off on the drive to work. So forgive us if we didn't get a chance to take every picture, every video, or get you every vaccination. "
- ―Lois telling Dewey why he has been neglected.
Lois and Dewey have a strained relationship and Dewey is extremely fearful of her. Lois on numerous occasions has completely ignored Dewey such as in "Malcolm's Job" when she didn't even know Dewey was absent from dinner and will harshly punish him when he breaks the rules such as in "Bowling". It is revealed that Lois has ignored Dewey since he was an infant as revealed in "Morp" when she tells Dewey she took almost no pictures of him when he was infant and even did not get him vaccinated and expresses no regret over it whatsoever. Dewey seems to dislike Lois to a degree as well and enjoys getting in trouble alongside his brothers and pissing her off, however he is the only one to recognize that Lois can be reasonable if you don't push her buttons. Dewey once even betrayed Lois in "Motivational Speaker" and began hanging out with a better mom but in the end got her name tattooed on his chest to prove that he does love her. Lois has on numerous occasions punished Malcolm and Reese for their poor treatment of Dewey and it is revealed that Lois believes that, besides Malcolm, Dewey is the only one of her children to amount to anything and claims he will drift through life into happiness.
- "So you're neglectful, and you think I'm an idiot. That's nice."
- ―Dewey to Hal after he attempts to pass false artwork to cheer Dewey up.
Hal and Dewey also have a strained relationship. Hal has on numerous occasions ignored Dewey and has even missed some of his birthdays as revealed in 'Malcolm's Girlfriend". Hal has underestimated Dewey on numerous occasions and does not seem to enjoy spending time with him much as revealed in 'Victor's other family" in which he misses Dewey's events on purpose, and Dewey even attempted to hide an activity from him in order to spare himself the disappointment of Hal missing it on purpose. In "Chad's Sleepover" Hal is extremely nasty to Dewey when he disobeys him despite the fact Dewey only disobeyed him once. Dewey seems to dislike the way his father treats him and in "Morp" was openly disgusted at him for attempting to pass false artwork to cheer Dewey up. Dewey has shown on a few occasions that he enjoys seeing Hal in misery and enjoys his misfortune. Hal does care for his son however and tried desperately to earn Dewey's love back after he refused to give Dewey piggy backs anymore. Dewey seems to prefer spending time with his dad than his mother due to her harsh personality and the two have gotten along on numerous occasions.
- The Buseys - Ever since Dewey got sent to The Busey class, he has been forced to make friends with them. Although Dewey hates being in the class, he likes the other kids there and considers them to be friends, who he genuinely cares about. Being the only kid who isn't actually emotionally disturbed, Dewey serves as the voice of reason for the entire class, and since the teacher doesn't give a crap about the kids and never does anything, Dewey is also the leader of the kids, hoping to teach them about not only academics, but the society of the real world. The Buseys legitimately want to solve their problems, and look up to Dewey for guidance. They all strongly rely on him and would be absolutely helpless without him.
- Hanson - Hanson is one of Dewey's friends in the Busey class. Dewey tries to help Hanson with his schizophrenia, tourette's syndrome, and belief that he's riding a motorcycle.
- Zoe -Zoe is one of Dewey's friends in the Busey class. Dewey tries to help Zoe with her belief that she can talk to animals and her ADHD.
- Chad - Chad is one of Dewey's friends in the Busey class. Dewey tries to help Chad with his haphephobia, schizophrenia, and obsession of biting people.
- Dewey felt a warm wave from the cracked microwave while in the womb. (Flashback)
- He has memories of being dropped as a baby by his grandparents. (The Grandparents)
- In "Garage Sale", it is hinted that Dewey has almost no positive childhood memories as shown when he finds his old baseball glove.
- In "Watching the baby", the story Dewey tells to baby Jamie about Lois and Hal being rich indirectly reveals that he believes that his parents make his life miserable on purpose. His story also reveals that he strongly desires having an unused pair of pants.
- Due to a misunderstanding, he is in a class for hopeless children in Dewey's Special Class and Malcolm felt terrible for it because of his mistake in letting Reese take the test for their brother. However, he lead the special needs class to rebel against the teacher. Dewy later got both Malcolm and Reese grounded by Lois for interfering with his test to keep him out of the Krelboyne class. Lois once got him out of there in "Buseys Run Away" when she had to explain to the counselor he was normal. However, he faked a mental relapse and was subsequently put back in the class.
- A semi-running gag that began in season 2 would be people having the tendency to forget about Dewey when he's supposed to be with them and eventually realizing that he's been gone for a long time. (i.e. Casino, Hal and Lois woke up and realized that the day before, they punished Dewey and he had to go stand in the corner. When they went back down into the kitchen, Dewey was propped up, face flat against the wall, sleeping, having been there the whole night. Later in the episode, Hal and the Wilkerson boys escaped a hotel casino and eventually got lost in the desert and were out there for hours. It wasn't until far into their adventure out there, that they realized that Dewey was gone the whole time.) This gag would have a great big blowout in the episode Morp, where Dewey gets forgotten, neglected, and completely ignored far more than usual, by Hal and Lois, and decides to get revenge on them by taking Hal's wallet and forcing them to go on a little scavenger hunt, to collect a bunch of party material, then leading them to an arcade place. When they get there, he tells them that he's not having the party be thrown for himself, but for Jamie, who still has time to live his life, unforgotten. Lois told him that this was a very nice and selfless gesture for him, but then grounds him for a week and takes a picture of his unhappied face, saying that now they have a wonderful memory of him.
- Dewey has many diseases involved with his ears due to the fact that he sticks dirty stuff in his ears and Reese gives him wet willies when he is annoyed with him.
- In Season 4's If Boys Were Girls, Dewey's female counterpart from Lois' fantasies was named Daisy (played by Jeannette McCurdy, who would later play a classmate of Dewey's named Penelope). Like Renee and Mallory, she loves shopping and likes to go to the mall everyday for new clothes. It was Daisy who told off Lois near the end of her fantasies that they're not above using her tactics against her because they're girls.
- He has written an opera about his parents arguing about a bed in Dewey's Opera and had the Busey Class involved in it.
- In the episodes No Motorcycles and Dewey's Dog, Dewey mentions that he is often beaten by both Reese and Malcolm.
- Dewey was exposed to a Flea Bomb while he was taking a nap in his bedroom. (Evacuation)
- His parents plan for him to have a life of luxury, unlike with the other boys. (Graduation)
- Dewey's actor Erik per Sullivan, is on twitter, see his account here.
- In Reese vs. Stevie it was shown that he was smoking but then finding out that his dad was smoking while he was quitting coffee he started to drink coffee.