J.K. Rowling’s middle initial is commonly said to represent Kathleen, her grandmother’s name.
Rowling was born Joanne Rowling and did not originally have a middle name beginning with K. When Bloomsbury prepared to publish her first Harry Potter book, the publisher suggested using initials rather than her full first name for the author credit.
Rowling chose K in tribute to her paternal grandmother, Kathleen Ada Bulgen Rowling. The resulting name, J. K. Rowling, became internationally associated with the Harry Potter novels. She has also published under the names Robert Galbraith and, for a later children’s book, Jo Rowling.
A frequent mix-up is the belief that the K stands for Rowling’s own legal middle name. It does not. The initial is part of her public author identity, while her birth name was Joanne Rowling.