Who is Claude Sawtelle from The Story of Edgar Sawtelle: A Novel and what is their importance?

Claude Sawtelle is the brother of Gar and uncle to Edgar. Claude is brash, impetuous, and lazy, and often clashes with his brother Gar. Claude worked for Doctor Papineau when he was younger, then leaves town to join the U.S. Navy. In Korea, Claude obtains a lethal poison used through injections. Claude later uses this poison to kill Gar.