Who is Tim Harrow from The Rifle and what is their importance?

Close to the present day of the novel (1993), Harrow inherits the Rifle from a gun show, and trades it to Harv Kline in exchange for fixing the fuel pump on his motor home. A "gun nut", Harrow loves weapons, is a member of the National Rifle Association, and is a fervent defender of the second amendment of the Constitution.