Sven Hjerson

Sven Hjerson is a fictional fictional detective in several books by Agatha Christie. He is not an actual character in the novels, but rather a character in books written by another character.

Hjerson is the most successful creation of Ariadne Oliver, a literary counterpart to Christie herself, and he is the fictional counterpart to Hercule Poirot, Christie's most famous literary detective. Comments by Ariadne Oliver about Hjerson are often read as (thinly disguised) comments by Christie about her characters, and specifically Poirot.

Christie is known to have often disliked Poirot's eccentric mannerisms, and the fact that he quickly became a much more successful character than any of her other detectives would become, with the possible exception of Miss Marple.

Hjerson's persona
Sven Hjerson is a detective star, the books sell very well and, as insinuated in the quote, a play about one of his adventures was organized. He seems to have fans, but his creator Ariadne Oliver dislikes (or even hates) the character. A reason for that is the fact that Sven has quite some following in his home country and people write corrections to her about him.

Hjerson is called a Finn, although his surname is neither Finnish nor even Scandinavian. He is also a vegetarian.