Hercule Poirot, of course, was Belgian, not French.
In colonial times and in the 19th century names from the Old Testament were very common. Isaac, Abraham, Ezekiel, Reuben, Hannah, Tamar, Rebecca, and many others. Around 1900 or earlier they went out of fashion. Supposedly the term "rube" comes from the idea of "Reuben" being a typical name a farmer might have.
I had a distant cousin in the 19th century who was called Parshandatha--it's a name from the book of Esther. In the Bible it's a man's name but it was bestowed on a girl. I figure they just opened the Bible at random and took the first name they saw, without reading the context to see that it was a male name.
Centuries back and even now, the mother’s maiden surname was used as a child’s first name. Though sometimes they used a grandmother or great grandmother’s surname if it had special meaning or was well know. That’s how there came to be several generations of men named Dummer Sewall. Yes, Dummer, I think it was a maternal great great grandmother’s maiden name, if I remember correctly.