Newt (Eddie Redmayne) was the main protagonist in the first movie Fantastic Beasts And Where To Find Them. This magizoologist came over to America with his case full of magical creatures, so he could release Frank, the Thunderbird, into the wilds of Arizona. Instead, he accidentally unleashed them all over New York City and got himself into trouble with the Magical Congress of the United States (MACUSA). He and his friends came across an Obscurial, a wizard who had developed a dark parasitic magical force. Despite their best efforts, they couldn’t save him. MACUSA presumedly killed him. After auror Percival Graves went on a rant about why wizards should live out in the open, the young Scamander realized that he might be someone else. He revealed Graves’s true identity: Gellert Grindelwald.
In Crimes of Grindelwald, Scamander is asked to go to Paris to track down the somehow-still-alive Credence and face Grindelwald if need be. This is extraordinarily difficult task is put on his shoulders by his former Hogwarts professor Albus Dumbledore. Scamander was expelled from Hogwarts, and Dumbledore argued against it, so Scamander kind of owes Dumbledore one. But this is certainly a big one.