Under what fictional author name did J.K. Rowling publish Quidditch Through the Ages?

J.K. Rowling published Quidditch Through the Ages under the fictional author name Kennilworthy Whisp.

The book is presented as a library volume about the history and rules of Quidditch, the broomstick sport played in the wizarding world. Rowling wrote it as a companion work to the Harry Potter series, imitating the style of a textbook that Hogwarts students might consult.

The original edition appeared in 2001 alongside Fantastic Beasts and Where to Find Them. Both books were published as charity works, with proceeds supporting Comic Relief. The fictional attribution adds to the impression that the reader is holding a genuine wizarding reference book.

Kennilworthy Whisp is different from Newt Scamander, the fictional author credited with Fantastic Beasts and Where to Find Them. Rowling herself is the real writer of both companion books, while Whisp and Scamander belong to the fictional world.