He's a fairly new character, created in 2008, but has only appeared in a couple of stories.
Adam Brashear debuted in the five issue Adam: Legend of the Blue Marvel mini-series created by Kevin Grevioux. A different version later appeared briefly in What If? Secret Invasion #1 (February 2010).
Was Adam The Blue Marvel in the Captain America and Bucky story that Brubaker wrote?
As for the book...the lineup doesn't really do anything for me.
I wish that a book called "MIGHTY Avengers" would be about the mightiest/strongest characters. It's kind of like "New Avengers" being called that - they aren't new, and they aren't even really Avengers. THAT book should be called Secret Avengers. THIS one could be called NEW Avengers.
I like the idea of there being this HUGE Avengers organization which is kind of how Hickman is doing it in the adjective-less book. Certain characters are used for certain missions and he does a great job of using the appropriate characters in the appropriate settings. You didn't see Hyperion going to the casino on a black ops mission.
I just wish the different books would have a specific direction or specialty and they had the appropriate characters. Granted we don't know a ton about this, but it doesn't seem to be the case here. It's just a bunch of people.
I'm a bit annoyed that there's now another Avengers title. I like the idea behind the book itself, but I thought Marvel would want to make it easy for fans of the movie to get into comics. With 8 Avengers titles now, it seems like it would be pretty overwhelming for new fans. Not to mention hard on the wallet.