Historical clue formulations

• Competitor of Peterson's and Princeton Review — 2020-10-30
• Giant in test prep — 2019-10-28
• Big name in test prep — 2017-12-31
• Giant in test prep — 2014-05-24
• "Mr. Clemens and Mark Twain" author Justin — 1998-03-15
• Film director Jonathan — 1994-12-24