Dewey is the second youngest son to Hal and Lois and younger brother to Francis, Reese and Malcolm and then now older then Jamie.
Dewey is quite timid, shy and a sweet young boy back when he was younger who lives under his shadow with his older brothers Malcolm and Reese tormenting and berating him.
Dewey is very deceiving and manipulative when comes to his character for getting back with Malcolm and Reese bullying him in the earlier seasons, even for his parents Hal and Lois and even being so annoying with others, but somehow he enjoys spending time with his father Hal and idolises him as a hero and father of the year he is.
He was quite misunderstood back in the early seasons often being neglected by his family in earlier Seasons 1-3, but now starting in Season 4 before Jamie is born, Dewey now grows up to communicate with his brothers more especially for Malcolm and Reese now respect him for how intelligent he is now and often join forces with them to manipulate their mother Lois more and sometimes less with their father Hal.
Since Dewey is becoming intelligent like Malcolm in later seasons, he is a talented musician for playing his own Piano as he won first prize in the contest due to his family objections and now he‘s becoming a mentor to his classmates in school known as Buseys since his brother Malcolm forced him to score his I.Q. very low and Dewey does what is best to tell Malcolm what a fraud he is and even with other family members.