Simplify the following text for a Grade 6 native English-speaking person.
Original: CÃ sar Estrada ChÃ vez ( ; March 31 , 1927 â `` April 23 , 1993 ) was an American farm worker , labor leader , and civil rights activist who , with Dolores Huerta , co-founded the National Farm Workers Association , which later became the United Farm Workers ( UFW ) .
Simplified: CÃ sar Estrada ChÃ vez ( March 31 , 1927 - April 23 , 1993 ) was the leader of a labor union .