Nova
The Nova Corps has played a role in the MCU thanks to Guardians of the Galaxy, but Nova himself hasn’t had his own big screen debut. While a variety of different characters have appeared in the Marvel Comics as Nova, the original hero is the only truly deserving of a solo film. Richard Rider was just a normal teenager who was given a huge responsibility—take the powers of the Nova Force and use them to defend earth and the rest of the universe.
As you can imagine, the journey from just an ordinary kid to being a superhero in charge of the well being of an entire universe is a rough transition but one that Rider took on valiantly. It’s enough to create an interesting origin story in movies and also make room to see Nova’s powers take center stage in dramatic combat.