Simplify the following text for a Grade 6 native English-speaking person.
Original: George Wald ( November 18 , 1906 â `` April 12 , 1997 ) was an American scientist who is best known for his work with pigments in the retina .
Simplified: George Wald ( November 18 , 1906 â `` April 12 , 1997 ) was an American scientist .