What does the “K” in J.K. Rowling’s name stand for?

The “K” in J.K. Rowling’s name stands for Kathleen.

Rowling was born Joanne Rowling and did not originally have a middle name. When Harry Potter and the Philosopher's Stone was prepared for publication, Bloomsbury asked her to use two initials because it was thought that a gender-neutral author name might appeal to young readers. She selected K in honor of her paternal grandmother, Kathleen.

The name therefore became J.K. Rowling rather than Joanne K. Rowling as a reflection of a birth certificate middle name. Rowling has also used other names professionally, including Robert Galbraith for her crime fiction.

The initial is easy to misremember as Katherine because that is a common spelling and name variant. The documented name associated with Rowling's paternal grandmother is Kathleen. This biographical detail is separate from the invented names and initials used by characters in the Harry Potter books.