Simplify the following text for a Grade 9 native English-speaking person.
Original: Ralph Waldo Emerson ( May 25 , 1803 â `` April 27 , 1882 ) was an American lecturer , philosopher , essayist , and poet , best remembered for leading the Transcendentalist movement of the mid-19th century .
Simplified: Ralph Waldo Emerson ( May 25 , 1803 â `` April 27 , 1882 ) was an American author , poet , and philosopher .