How does Oscar's character change throughout the story?
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.