Credence is known to be an important character in Fantastic Beasts. He is a troubled individual who has always been fascinated with Dark Magic. He started to want to learn more about Grindelwald who is known to be an obscurus. For people who are not sure what this is, this is the term used in order to describe the type of magic that was not used up so it has become bad.
This occurs when the wizard fails to use or tries to hide magical powers. Without Credence, the story will not be as exciting. There are a lot of people who are interested in this probably because it is related to the Harry Potter series.