Simplify the following text for a Grade 9 native English-speaking person.
Original: William Clarke Quantrill ( July 31 , 1837 -- June 6 , 1865 ) , was a Confederate guerrilla leader during the American Civil War .
Simplified: William Clarke Quantrill ( July 31 , 1837 â `` June 6 , 1865 ) , was a Confederate leader during the American Civil War .