Rex Fortescue was the thoroughly unpleasant patriarch of the Fortescue family and the first victim to die in A Pocket Full of Rye. Always a business man of questionable ethics, his judgement was becoming equally questionable, to the damage of his company, until somebody saw fit to get him out of the way - permanently.
His second marriage was childless. His second wife was thirty years younger than him. He had met her at Brighton, where she had been a manicurist.
His father hailed from Central Europe and had been named Fontescu.
Rex was a "large flabby man with a gleaming bald head". He was in the habit of wearing "loosely cut country tweeds in his city office". According to Inspector Neele, he had certain connections with the black market and put through a few questionable deals, but they had always been just inside the law.
Many years before the events of the novel, Rex had gone to Africa with Mr MacKenzie, to survey the Blackbird Mine. Mr MacKenzie had died while there, and Rex had come back saying that the mine was worthless. Mrs MacKenzie said that it was her husband's mine, and she was convinced that Rex was responsible for his death.
In the year and a half before his death, Rex had seemed a changed man. He had become flamboyant and bombastic, and had been selling good stock, and making speculative investments. This caused conflict between him and his son Percival. Percival wanted him to see a doctor, but Rex refused.
Rex was suddenly taken ill at his office, and was taken to St Jude's Hospital, where he died. Professor Bernsdorff was of the opinion that he was poisoned with taxine. Some rye was found in the right hand pocket of his jacket. It is later revealed that taxine was put into the marmalade which Rex had eaten at breakfast.
In the BBC 1985 adaptation of the novel which formed part of the Miss Marple series, the part of Rex Fortescue is played by Timothy West. In this adaptation, he does ask for his tea ahead of schedule but dies before drinking anything, thus eliminating his secretary Irene Grosvenor, who prepared the tea, as a suspect.
In the ITV 2008 adaptation of the novel (Episode 1, Season 4 of Agatha Christie's Marple), the part of Rex Fortescue is played by Kenneth Cranham. Here the mental illness he was suffering from was said to be Pick's disease, a form of dementia. He dies after drinking the tea at the office in the same way as in the original novel.