Which of these Agatha Christie characters has appeared in the most of her novels?

Hercule Poirot is a fictional Belgian detective, created by Agatha Christie. Poirot is one of Christie's most famous and long-lived characters, appearing in 33 novels, one play (Black Coffee), and more than 50 short stories published between 1920 and 1975.

Poirot's name was derived from two other fictional detectives of the time: Marie Belloc Lowndes' Hercule Popeau and Frank Howel Evans' Monsieur Poiret, a retired Belgian police officer living in London.

Poirot also bears a striking resemblance to A. E. W. Mason's fictional detective, Inspector Hanaud of the French Sûreté, who first appeared in the 1910 novel At the Villa Rose and predates the first Poirot novel by ten years.

Jane Marple, usually referred to as Miss Marple, is a fictional character appearing in 12 of Agatha Christie's crime novels and in 20 short stories. Miss Marple is an elderly spinster who lives in the village of St. Mary Mead and acts as an amateur consulting detective.

Ariadne Oliver and Parker Pyne only appear in a handful of Agatha Christie novels or short stories.