The “K” in J.K. Rowling’s pen name stands for Kathleen. Rowling was born Joanne Rowling, and Kathleen was her paternal grandmother’s name.
Rowling did not originally have a middle name. Her publishers asked her to use two initials because they believed a gender-neutral author name might appeal to boys as well as girls. She selected “K” in honor of Kathleen, creating the name J.K. Rowling.
The author is often called “Jo Rowling” in personal and professional contexts. The “J” stands for Joanne, her given name. Rowling has said that she was never legally named Joanne Kathleen Rowling at birth, despite that form sometimes appearing in references.
Her books were marketed under J.K. Rowling internationally. After publishing crime novels, she used the pseudonym Robert Galbraith, while continuing to use J.K. Rowling for the Harry Potter series and related works.