At the beginning, Oscar is portrayed as being predominantly interested in girls, and this is something that does not change throughout the book, but merely grows in intensity. After going from having two girlfriends to being single, Oscar falls into a love affair with food and role-playing games, leading him to be cast at school as an overweight geek.

By the time he reaches university, Oscar is still considered a geek, and his sister Lola entreats a former partner, Yunior, to be his friend and keep an eye on him.

Repeated heartbreak and rejection eventually lead Oscar to an unsuccessful suicide attempt, after which he eventually begins to briefly feel more positive.

Later, he lands a teaching job at his alma mater, where he once again finds himself the subject of ridicule.

After being badly beaten while on holiday in Santo Domingo, Oscar begins to wonder if there is truth in the idea of the fuku curse which is said to exist over his life.

The final stage of Oscar's character development is a disturbing one, in which he aggressively stalks a woman in the Dominican Republic. This ultimately leads to him once again getting beaten up, having seemingly not learnt his lesson. Ultimately, Oscar's strange and obsessive ways do not abate—rather, they cost him his life.

According to Junot Diaz, every Dominican male should be physically attractive. He must have a machismo attitude and demonstrate considerable sexual prowess. Oscar’s character fails to live up to these standards. His subtle masculinity does not find favor with women. Disastrously overweight and unwilling to change, Oscar fails to engage in romantic relationships throughout the narrative, and is consistently displaced into the "friend zone."

Oscar's weight contributes to his low self-esteem and makes him vulnerable to depression. He struggles with mental health issues, self-destructive behavior, and suicide attempts. As Oscar matures, he becomes an introvert. He prefers to stay at home reading fantasy novels or writing science fiction stories. His inability to fit into the Latino culture alienates him from society.

As Oscar fails to achieve his life goals, he questions the cause of his misfortune. He attributes his bad luck to a family curse. At the end of the novel, Oscar realizes that there is no escape. He decides to risk it all in the name of love. The tragic hero pays the price for his inability to conform to a set of expected ideals. He succumbs to a horrific death.

In Junot Diaz's The Brief Wondrous Life of Oscar Wao, Oscar is a quester, first for women and then for love.  In between, he redefines himself and his quest as he learns more about himself, his family, and the fuku curse.

At first, young Oscar is a player, following what the machismo culture expects of males.  He juggles two girls at once, but after he gets rejected, he balloons up in weight and becomes a ghetto nerd.

His next quest is to become the next J.R.R. Tolkien, fantasy fiction writer extraordinaire.  His stories are good, but the better he gets at writing them, the fatter he gets.  And the fatter he gets, the further away from finding a girl (and love) he gets.

Oscar realizes he must die to end his family's curse.  So he returns to the D.R., where he meets a prostitute, falls in love, and gets so close to the fuku that it kills him.  He then becomes a kind of sacrificial hero (Christ-figure) whose death ends the curse and thus protects his sister and future generations from it.

His death influences the book's main narrator, Yunior.  So, even in death, Oscar becomes a teacher and mentor, an influence on his macho former-roommate.  Yunior ends up becoming what Oscar wanted all along, a teacher and an author of Oscar's book.  In this way, Oscar is Yunior's doppelganger, or ghostly twin.