Jonathan Clark is the older brother to a fellow soldier who was what? 
Jonathan Clark (soldier):  He was the older brother of fellow soldier General George Rogers Clark and of Captain William Clark of the Lewis and Clark Expedition. George Rogers Clark: George Rogers Clark (November 19, 1752 – February 13, 1818) was a surveyor, soldier, and militia officer from Virginia who became the highest ranking American military officer on the northwestern frontier during the American Revolutionary War.
surveyor, soldier, and militia officer