Newt Scamander is credited as the author of Rowling’s Fantastic Beasts textbook.
Fantastic Beasts and Where to Find Them first appeared in 2001 as a companion book to the Harry Potter series. Its fictional author is Newton “Newt” Scamander, a magizoologist who studies magical creatures. The book is presented as a Hogwarts textbook, complete with notes attributed to Harry, Ron and Hermione.
Rowling later developed Newt into the central character of a film series. The screenplay for Fantastic Beasts and Where to Find Them was written by Rowling and released as a film in 2016, with Eddie Redmayne playing Newt. The film is set decades before the main Harry Potter story and follows Newt in 1920s New York.
Newt Scamander is not the same person as Rubeus Hagrid, who teaches Care of Magical Creatures at Hogwarts for part of the series. Hagrid is an important creature enthusiast, but Newt is the fictional textbook author named on the book’s title page.