Newt Scamander is the fictional textbook author behind Fantastic Beasts and Where to Find Them.
In J.K. Rowling’s wizarding world, Newt Scamander wrote the book as a guide to magical creatures. Hogwarts students use it as a school textbook, and Harry Potter’s copy is described as bearing notes and doodles from Harry and Ron. The book was published in the real world in 2001 as a charity companion volume.
Scamander later became the central character of the Fantastic Beasts film series. Those films portray him as a magizoologist who travels with magical creatures and becomes involved in conflicts involving Gellert Grindelwald and Albus Dumbledore.
Newt Scamander is therefore both an in-universe author and a fictional protagonist connected to a separate film storyline. He should not be confused with the actor Eddie Redmayne, who portrays him in the films.