Oh, Shreve. Feisty, feisty Shreve. Quentin's roommate at Harvard, this guy – while a little grating – is pretty important. Why? Because he's from the North (Canada). What's that we say? The North?! But really, the fact that Quentin isn't a Southerner allows him a different perspective on things: one that's maybe not as wrapped up in all the drama. Maybe.
As much as he is interested in having Quentin "Tell about the South," Shreve also wants to give his own version of the story. He's the one, for example, who implies that Charles went along with Henry's plan only so Sutpen would admit that he was Charles' father. All of his ideas are made-up, yet he bears a heavy influence on the story and what we know of Sutpen.
And unlike Mr. Compson – another of our many narrators – Shreve does not characterize Sutpen as a heroic figure. His outsider status gives him a distance compared to the other narrators, and his involvement in the story is skeptical, rather than romantic and personal. In a world full of Sutpen drama, it's nice to have this little break, care of Mr. Harvard North.