Roald Dahl (/ˈroʊ.ɑːl ˈdɑːl/; Norwegian pronunciation: [ˈɾuːɑl dɑl]; 13 September 1916 – 23 November 1990) was a British novelist, short story writer, poet, screenwriter, and fighter pilot. His books have sold over 200 million copies worldwide.

Born in Wales to Norwegian parents, Dahl served in the Royal Air Force during the Second World War, in which he became a flying ace and intelligence officer, rising to the rank of acting wing commander. He rose to prominence in the 1940s with works for both children and adults and he became one of the world's best-selling authors. He has been referred to as "one of the greatest storytellers for children of the 20th century". His awards for contribution to literature include the 1983 World Fantasy Award for Life Achievement, and the British Book Awards' Children's Author of the Year in 1990. In 2008, The Times placed Dahl 16th on its list of "The 50 greatest British writers since 1945".

Dahl's short stories are known for their unexpected endings and his children's books for their unsentimental, macabre, often darkly comic content, featuring villainous adult enemies of the child characters. His books champion the kind-hearted, and feature an underlying warm sentiment. Dahl's works for children include James and the Giant Peach, Charlie and the Chocolate Factory, Matilda, The Witches, Fantastic Mr Fox, The BFG, The Twits and George's Marvellous Medicine. His adult works include Tales of the Unexpected.

Roald Dahl died on 23 November 1990, at the age of 74 of a blood disease, myelodysplastic syndrome, in Oxford, and was buried in the cemetery at St Peter and St Paul's Church in Great Missenden, Buckinghamshire, England. According to his granddaughter, the family gave him a "sort of Viking funeral". He was buried with his snooker cues, some very good burgundy, chocolates, HB pencils and a power saw. Today, children continue to leave toys and flowers by his grave. In November 1996, the Roald Dahl Children's Gallery was opened at the Buckinghamshire County Museum in nearby Aylesbury.

In 2002, one of Cardiff Bay's modern landmarks, the historic Oval Basin plaza, was re-christened "Roald Dahl Plass". "Plass" means "place" or "square" in Norwegian, referring to the acclaimed late writer's Norwegian roots. There have also been calls from the public for a permanent statue of him to be erected in Cardiff. In 2016, the city is to celebrate the centenary of Dahl's birth in Llandaff. Welsh Arts organisations, including National Theatre Wales, Wales Millennium Centre and Literature Wales, have come together for a series of events, titled Roald Dahl 100, including a Cardiff-wide City of the Unexpected, which will mark his legacy.

Dahl's charitable commitments in the fields of neurology, haematology and literacy during his life have been continued by his widow since his death, through Roald Dahl's Marvellous Children's Charity, formerly known as the Roald Dahl Foundation. The charity provides care and support to seriously ill children and young people throughout the UK. In June 2005, the Roald Dahl Museum and Story Centre in the author's home village Great Missenden was officially opened by Cherie Blair, wife of UK Prime Minister Tony Blair, to celebrate the work of Roald Dahl and advance his work in literacy education. Over 50,000 visitors from abroad, mainly from Australia, Japan, the United States and Germany, travel to the village museum every year.

In 2008, the UK charity Booktrust and Children's Laureate Michael Rosen inaugurated The Roald Dahl Funny Prize, an annual award to authors of humorous children's fiction. On 14 September 2009 (the day after what would have been Dahl's 93rd birthday) the first blue plaque in his honour was unveiled in Llandaff. Rather than commemorating his place of birth, however, the plaque was erected on the wall of the former sweet shop (and site of "The Great Mouse Plot of 1924") that features in the first part of his autobiography Boy. It was unveiled by his widow Felicity and son Theo. The anniversary of Dahl's birthday on 13 September is celebrated as "Roald Dahl Day" in Africa, the United Kingdom and Latin America.

In honour of Roald Dahl, the Royal Gibraltar Post Office issued a set of four stamps in 2010 featuring Quentin Blake's original illustrations for four of the children's books written by Dahl during his long career; The BFG, The Twits, Charlie and the Chocolate Factory, and Matilda. A set of six stamps was issued by Royal Mail in 2012, featuring Blake's illustrations for Charlie and the Chocolate Factory, The Twits, The Witches, Matilda, Fantastic Mr Fox, and James and the Giant Peach. Dahl's influence has extended beyond literary figures. For instance film director Tim Burton recalled from childhood "the second layer [after Dr. Seuss] of connecting to a writer who gets the idea of the modern fable – and the mixture of light and darkness, and not speaking down to kids, and the kind of politically incorrect humour that kids get. I've always like that, and it's shaped everything I've felt that I've done." Actress Scarlett Johansson named Fantastic Mr Fox one of the five books that made a difference to her.

Regarded as "one of the greatest storytellers for children of the 20th century", Dahl was named by The Times one of the 50 greatest British writers since 1945. He ranks amongst the world's best-selling fiction authors with sales estimated at over 200 million, and his books have been published in almost 60 languages. In 2003 four books by Dahl, led by Charlie and the Chocolate Factory at number 35, ranked among the Top 100 in The Big Read, a survey of the British public by the BBC to determine the "nation's best-loved novel" of all time. In surveys of UK teachers, parents and students, Dahl is frequently ranked the best children's writer. In a 2006 list for the Royal Society of Literature, Harry Potter creator J. K. Rowling named Charlie and the Chocolate Factory one of her top ten books every child should read. In 2012, Matilda was ranked number 30 among all-time best children's novels in a survey published by School Library Journal, a monthly with primarily U.S. audience. The Top 100 included four books by Dahl, more than any other writer: Matilda, Charlie and the Chocolate Factory, The Witches, and The BFG.