Historical clue formulations

• "Murder on the Orient Express" detective — 2019-10-08
• Agatha Christie once described him as a "detestable, bombastic, tiresome little creature" — 2017-11-11
• Recurring character who dies in the novel "Curtain" — 2007-10-12
• Herculean literary character? — 2006-07-16
• User of "little gray cells" — 2000-10-06
• Christie creation — 1999-05-09
• Mustachioed detective — 1997-05-25