Simplify the following text for a Grade 12 native English-speaking person.
Original: Pedro Antonio MarÃ n MarÃ n ( May 13 , 1930 ( disputed ) - March 26 , 2008 ) , known by his `` nom de guerre '' Manuel Marulanda VÃ lez , was the main leader of the FARC-EP ( `` Fuerzas Armadas Revolucionarias de Colombia - EjÃ rcito del Pueblo '' ) .
Simplified: Pedro Antonio MarÃ n , ( 1930-2008 ) known by his pseudonym , Manuel Marulanda VÃ lez , and nicknamed by his comrades `` Tirofijo '' , apparently because of a reputed ability to accurately aim firearms . He was the main leader of the FARC-EP ( `` Fuerzas Armadas Revolucionarias de Colombia - EjÃ rcito del Pueblo '' ) .