Mrs Castle

In the novel Evil Under the Sun, Mrs Castle is the owner and proprietor of the Jolly Roger Hotel on Smugglers' Island in Devon. A Londoner, Mrs Castle is described as "a  woman  of forty  odd  with  a  large  bust,  rather  violent  henna  red  hair,  and  an  almost  offensively refined  manner  of  speech." Christie depicted her affected way of speaking with examples such as "Ay am sure" and "the  quayettest  place  imaginable".

1982 film
In the 1982 Evil Under the Sun John Brabourne/EMI film, the character is named "Daphne Castle" and is portrayed by Maggie Smith. Here her backstory is considerably enhanced. She is a former mistress of the King of Tyrania. Her hotel is located on an island in the Mediterranean of the coast of Tyrania and she was given the hotel and island as a gift by the King. Daphne is also a friend and former lover of Kenneth Marshall and there is therefore considerable tension between her and Arlena Stuart Marshall.

Agatha Christie's Poirot
In the ITV 2001 adaptation, Mrs Castle is portrayed by Rosalind March. Here the hotel is a health resort and Mrs Castle, besides running the hotel, is a health therapist. She has her own recipe for a nettle water drink and recommends steam cabinet treatment for Poirot.