Who is Corporal Merriell A. "Snafu" Shelton from With the Old Breed, at Peleliu and Okinawa and what is their importance?

Corporal Merriell A. Shelton is an enlisted marine and a veteran of Cape Gloucester. He is from Louisiana and is the gun captain and nearly-constant companion of Sledge. Surprisingly, little biographical data are offered for Shelton other than that he smokes, has a good sense of humor, and is a typical marine in most respects. Sledge admires him and finds his company enjoyable.