Simplify the following text for a Grade 11 native English-speaking person.
Original: Henry David Thoreau ( born David Henry Thoreau ; July 12 , 1817 â `` May 6 , 1862 ) was an American author , poet , abolitionist , naturalist , tax resister , development critic , surveyor , historian , philosopher , and leading transcendentalist .
Simplified: Henry David Thoreau ( born David Henry Thoreau ; July 12 , 1817 - May 6 , 1862 ) was an American author , naturalist and philosopher .