The “K” in J.K. Rowling stands for Kathleen, the first name of her paternal grandmother. Rowling was born Joanne Rowling, without a middle name, and adopted the initial for her publishing name.
When the first Harry Potter book was prepared for publication, Rowling’s publisher reportedly wanted a name using initials rather than her full first name. The chosen format became J.K. Rowling, with “J” representing Joanne and “K” representing Kathleen.
Readers sometimes assume that Kathleen was Rowling’s own given middle name. It was not: she added the initial as a tribute to her grandmother. Rowling has also used other names professionally, including Robert Galbraith for crime novels.
The author’s legal name has changed at different points in her life, but “J.K. Rowling” remains the internationally recognized name associated with Harry Potter. The initials also helped the books appeal broadly without signaling the author’s gender to prospective readers.