The “K” in J.K. Rowling stands for Kathleen.
Rowling was born Joanne Rowling without a middle name. When Bloomsbury prepared Harry Potter for publication, the publisher requested two initials rather than using her first name alone. Rowling chose K in honour of her paternal grandmother, Kathleen, creating the name J.K. Rowling.
This detail is often misstated as Katherine or confused with a birth middle name. Kathleen was not originally part of Rowling’s legal birth name; it was selected as a publishing middle initial. The name therefore reflects a family tribute as well as a marketing decision.
Rowling has also published adult fiction under other names. The Cormoran Strike novels use Robert Galbraith, while The Casual Vacancy was published under J.K. Rowling. These different bylines do not change the origin of the initials used for the Harry Potter books.