What is J.K. Rowling’s middle initial commonly expanded to?

J.K. Rowling’s middle initial is commonly expanded to Kathleen.

She was born Joanne Rowling, without a middle name. When Bloomsbury prepared to publish Harry Potter and the Philosopher’s Stone, the publisher believed that a name with two initials might appeal to a broad readership, particularly boys. Rowling therefore adopted the initial K, taken from Kathleen, the first name of her paternal grandmother, and became J.K. Rowling in publication.

The name is often misidentified as Katherine because Katherine is a familiar expansion of K. Rowling herself has explained that Kathleen was chosen as a family reference. Her legal name later changed through marriage, but J.K. Rowling remained the professional name associated with her fantasy fiction.

This naming detail is also distinct from the pen name Robert Galbraith, which she used for the Cormoran Strike crime novels. The initial-based name appeared on the Harry Potter books from the beginning, while Robert Galbraith was introduced much later as a separate author identity.