Gary R. Gruber is an American theoretical physicist, educator, and author who has written many books and software programs for standardized test preparation. His work focuses on test-taking and critical thinking skills and claims sales of more than 7 million books. His writings include the Gruber's Complete Guide series as well as books and columns of brain teaser puzzles and other articles. He also works with schools, school districts, state departments of education and other educational organizations in the development of testing and critical thinking skills and educational motivation programs. [More at Wikipedia]

United States of America