From the Bronx Community College's webpage for the Hall of Fame:

Actor Edwin Booth

William Cullen Bryant

Oliver Wendell Holmes

Samuel Langhorne Clemens (Mark Twain)

To read the complete article, see:
Elementary's Holmes and Watson at the Hall of Fame for Great Americans (http://fourthgarrideb.com/2016/06/elementarys-holmes-and-watson-at-the-hall-of-fame-for-great-americans/)

For more information on the series, see this 2012 article from Dick Johnson's MedalBlog:
Hall of Fame Series - The Most Successful Medal Program (https://medalblog.wordpress.com/2012/12/03/hall-of-fame-series-the-most-successful-medal-program/)