Lamentations And Invocations

When reading some Saint short stories by Leslie Charteris, I noticed similarities between Simon Templar and Poul Anderson's Dominic Flandry. Then I remembered that Hank Davis did state in a The Technic Civilization Saga introduction that Anderson had intended Flandry to be an sf counterpart to Templar. Next, I will quote an account of another famous fictional character while omitting the character's name:

"I pass over the spectacle of [name] on a camel. He started by groans and lamentations and ended by shrieks, gesticulations and invocations to the Virgin Mary and every Saint in the calendar."

Although this reads exactly like Anderson's Nicholas van Rijn, the source is:

Agatha Christie, "The Adventure of the Egyptian Tomb" IN Christie, Poirot Investigates (London, 1981), pp. 92-109 AT p. 98.

Three more comparisons and then some differences. First, Poirot says:

"'The true clues are within - here!' He tapped his forehead. 'See you, I need not have left London. It would have been sufficient for me to sit quietly in my rooms there. All that matters is the little grey cells within.'"

-Agatha Christie, "The Kidnapped Prime Minister" IN Poirot Investigates, pp. 129-151 AT p. 144.

Van Rijn says:

"'...tonight I have been on Cain up here, in this old brain, and it is rusty and afloat in alcohol but it has stored away more information about the universe than maybe the universe gets credit for holding.'"

-Poul Anderson, "The Master Key" IN Anderson, Trader To The Stars (New York, 1964), pp. 115-159 AT pp. 153-154.

Secondly, the Belgian Poirot's turns of phrase confirm that he is not a native English speaker. Van Rijn at least pretends to have trouble with Anglic but what would his first language have been?

Thirdly, both series commence with their central character advanced in years. Poirot has retired from the Belgian Police before becoming a private investigator and van Rijn approaches an age when he has to stay at home and send younger men into space.

Differences

Poirot is usually composed. His distress when seasick or riding a camel is unusual but genuine. By contrast, van Rijn habitually shrieks, gesticulates and invokes but this is often if not always an act to project a dynamic image while making his enemies underestimate him. 

Secondly, although van Rijn avoids violence, he is able to handle himself in combat, a situation that Poirot never has to face.