Brinker plays a secondary role in the novel as Gene's inquisitor before and during the Assembly Room trial. His public performance in the Assembly Room represents his most dramatic moment; aggressive, but scrupulously polite, he pursues responsibility irresponsibly.
A successful, conventional student leader, Brinker stands in contrast to both Finny (the unconventional leader) and Gene (the unquestioning follower). Smooth and carefully dressed, Brinker strives to impress people and, when he can, exercise control over them.
The glimpse of Brinker's father in the last chapter throws some light on Brinker's character. The son of an overbearing father, Brinker develops his aggressive tendencies in self-defense; he manipulates and bullies people to avoid being manipulated or bullied himself.
In fact, Brinker uses his manipulative powers to compete with Finny for Gene's loyalty. Brinker senses Gene's dark secret — that he envies and resents Finny — and tries to exploit it by needling him about his friend. Brinker's manipulation takes an especially cruel turn as he escalates his needling into the trial in the Assembly Room. Here his motivation seems strangely similar to Gene's own in causing Finny to fall. Indeed, as the story dramatizes, affection — and even love — can become harmful and finally destructive in the emotionally charged atmosphere of a boys' prep school.
By the last chapter, Brinker seems less aggressively competitive — but, of course, Finny is dead now, and the competition is over. Brinker actually comes around to profess a version of Finny's conspiracy theory about the war and even produces a chief example in the person of his own father, who seems to be one of those fat and foolish old men behind the war.
Yet Brinker seems less mature in the last chapter than Gene, who can now view Mr. Hadley with tolerance and even pity. In fact, Brinker functions here as a kind of measure by which the reader can gauge Gene's growth toward adulthood after he comes to terms with Finny's death and his own culpability.