J.K. Rowling’s first name is Joanne.
She was born Joanne Rowling. Her published name uses the initials J.K. Rowling, although the middle initial was not part of the name given at birth. Bloomsbury requested a two-initial author name for the Harry Potter books, partly because the publisher believed some boys might be less likely to choose a book if they knew it was written by a woman.
The K stands for Kathleen, the name of Rowling’s paternal grandmother. Rowling has no recorded middle name of Kathleen herself, but she adopted the initial for her professional author identity. The name J.K. Rowling therefore combines her given name with a family tribute and a publishing decision.
She is also sometimes called Jo by friends and readers. Robert Galbraith is a separate pseudonym used for her crime fiction, while Newt Scamander is a fictional character and in-universe author, not another name for Rowling.