He married American actress Patricia Neal in 1953 and they had a total of five children together.
Their first baby was named Olivia Twenty. Why?
Olivia Twenty was born in New York on April 20, 1955, and named after her mother’s favorite Shakespearean heroine, the date of her birth, and the fact that Roald had $20 in his pocket when he came to visit Pat in the hospital.
And their second child, originally called Chantal Sophia, ended up getting a name change:
A few days after Chantal had been christened, Roald realized her name rhymed with Dahl and renamed her Tessa.
The last three three Dahl children were named Theo Matthew, Ophelia Magdalena, and Lucy Neal. My guess is that Ophelia is another Shakespeare reference, and that Sophia and Magdalena came from Dahl’s mother, Sofie Magdalene. I’m not sure what inspired the other names.
[Sadly, Olivia Twenty died of the measles in 1962, before a reliable measles vaccine had been developed.]
Source: Sturrock, Donald. Storyteller: The Authorized Biography of Roald Dahl. New York: Simon & Schuster, 2010.