In the novel Death on the Nile, Doctor Carl Bessner is a famous physician, with a large clinic in Czechoslovakia, and a European reputation as a fashionable physician. He attends to Simon Doyle after Jacqueline de Bellefort shot him in the leg. One of his surgical blades is used to kill Louise Bourget.
The text does not state his nationality precisely but Bessner himself says he is well-known all over Austria. Mrs Allerton thinks that he is German and Simon Doyle described him as "very German".
When trying to match the names on the passenger list to the faces in the dining room, Mrs Allerton describes Dr Bessner as "the fat one with the closely shaved head and the moustache". He wears spectacles with thick lenses.
Dr Bessner is present during the denouement, along with Cornelia Robson.
At the end of the novel, Bessner proposes to, and later marries, Cornelia. He had earlier stated that she was a "very nice maiden", who has "the nice curves". He also said that she listened very intelligently, and that it was a pleasure to instruct her.
In the 1978 Ustinov film adaptation, Bessner's first name is changed to "Ludwig". He is from the Bessner Institute in Zurich. He is portrayed by Jack Warden. Unlike in the original novel, Bessner here had a motive which made him a plausible suspect. Linnet Doyle had criticised his clinic and his medical methods openly to people of influence. In particular, he had prescribed a course of "armadillo's urine" to her friend Myra Seligman and she went "barking mad".