Raymundus Joannes de Kremer was a Flemish Belgian writer who used the pen names John Flanders and Jean Ray. He wrote both in Dutch and French.

He was born in Ghent, his father a minor port official, his mother the director of a girls' school. Ray was a fairly successful student but failed to complete his university studies, and from 1910 to 1919 he worked in clerical jobs in the city administration.

By the early 1920s he had joined the editorial team of the Journal de Gand. Later he also joined the monthly L'Ami du Livre. His first book, Les Contes du Whisky, a collection of fantastic and uncanny stories, was published during 1925.

During 1926 he was charged with embezzlement and sentenced to six years in prison, but served only two years. During his imprisonment he wrote two of his best-known long stories, The Shadowy Street and The Mainz Psalter. From the time of his release in 1929 until the outbreak of the Second World War, he wrote virtually non-stop.

Between 1933 and 1940, he produced over a hundred tales in a series of detective stories, The Adventures of Harry Dickson, the American Sherlock Holmes. He had been hired to translate a series from the German, but he found the stories so bad that he suggested to his Amsterdam publisher that he should re-write them instead. The publisher agreed, provided only that each story be about the same length as the original, and match the book's cover illustration. The Harry Dickson stories are admired by the film director Alain Resnais among others. During the winter of 1959-1960 Resnais met with Ray in the hope of making a film based on the Harry Dickson character, but nothing came of the project.

During the Second World War Ray's prodigious output slowed, but he was able to publish his best works in French, under the name Jean Ray: Le Grand Nocturne (1942), La Cité de l'Indicible Peur, also adapted into a film starring Bourvil, Malpertuis, Les Cercles de L'Epouvante (all 1943), Les Derniers Contes de Canterbury (1944) and Le Livre des Fantômes (1947).

After the war he was again reduced to hackwork, writing comic-strip scenarios by the name of John Flanders. He was rescued from obscurity by Raymond Queneau and Roland Stragliati, whose influence got Malpertuis reprinted in French during 1956.

A few weeks before his death, he wrote his own mock epitaph in a letter to his friend Albert van Hageland: Ci gît Jean Ray/homme sinistre/qui ne fut rien/pas même ministre ("Here lies Jean Ray/A man sinister/who was nothing/not even a minister").