It's very easy to get excited about Dunkirk, director Christopher Nolan's upcoming sweeping British war epic, for a number of reasons. Perhaps the main reason there's such a great amount of curiosity right now is due to the character who Harry Styles plays in Dunkirk, Alex, and who he is in regards to the rest of the cast. The first handful of trailers, at least, definitely make it seem like Alex is going to have a very tough time on the beaches at Dunkirk.
In one of the earliest trailers, we catch a glimpse of Alex sitting with two of his friends and fellow soldiers. All three young men was another man take off his gear and walk straight into the English Channel; definitely an omen of bad things to come. In a later trailer, we see Alex in a British ship with his fellow soldiers as they try to avoid being caught or sunk by the Germans. So yeah, it's probably safe to assume that Alex, the young and handsome British soldier, is going to be put through hell in Dunkirk.
As of right now, it's safe to just assume the basics — that Alex is a British soldier and he may or may not live through the evacuation at Dunkirk. Other details may get lost in the mix if only because he is part of a larger cast with plenty of famous British faces including Kenneth Branagh, Mark Rylance, Tom Hardy, and James D'Arcy. With that large and acclaimed a cast, there's just not enough room to explain who every character is thoroughly.
It's also known that Styles was one of thousands that auditioned for Alex. People magazine quotes Nolan about how he chose Styles: "[F]or the guys on the beach, we really wanted young unknowns. [Styles] is not that unknown, but he’d never done anything as an actor before. So he auditioned. I auditioned literally thousands of young men with different combinations of young men. And he had it."
This intense audition process gives the impression that Alex might be a more important character than we realize, because why go through the hassle of auditioning thousands of young actors for what otherwise sounds like a supporting, background-type role?
Finally, it's worth noting that this role could lead to future bigger things for Styles. As he forges his own solo career in a post-One Direction world, the chance to receive favorable reviews for his performance could open the door to other projects. Not too shabby for a young man who's acting in his first major motion picture, eh?