One thing that's been interesting about the MCU is that secret identities have never really been important.
So yeah, I can't really think of any important character with a secret identity. Closest is Spidey's whose was only barely a secret anyway, and that only lasted two movies. On the other hand, you could argue that secret IDs are overdone and not really having them refreshing. But I'd be curious to see how the MCU would handle a character that REALLY would rather their identity not be known.
- Iron Man? Revealed his identity publicly at the end of his first movie.
- Cap? Never had a secret identity.
- Hulk? I'm pretty sure he's publicly known as Banner.
- Thor? Just Thor.
- Black Widow and Hawkeye? Just secret agents who work for Shield.
- Black Panther? Identity is basically public.
- Spidey? Had his identity revealed at the end of his last movie.
- Dr. Strange? That's his actual name.
- Captain Marvel? Another public hero.
- Ant-Man? Nobody really cares who he is.
So yeah, I can't really think of any important character with a secret identity. Closest is Spidey's whose was only barely a secret anyway, and that only lasted two movies. On the other hand, you could argue that secret IDs are overdone and not really having them refreshing. But I'd be curious to see how the MCU would handle a character that REALLY would rather their identity not be known.