Capitan America The First Avenger (even though he wasn't a founding member of the avengers), is the story of young Steve Rogers during WW2.
Steve is one of those people with a lot of patriotic pride, and is wants nothing more to serve his country, simply because he can't stand bullies. However, with his super skinny frame, asthma, and various other medical conditions, he's always getting beat up. Plus the army won't take him, so there's that.
So he's left moping until a scientist offers him a chance. He injects him with the Super Solider serum, which brings him to the peak of human capabilities, and amplifies the good or evil of a person.
Steve rogers is now Capitan America, and leads the fight against a Nazi science division called Hydra lead by the Red Skull, who was injected with a prototype serum.
All in all, this is a good movie, filled with lots of action, humor, and references to other marvel movies (by the way, Stan Lee is a 4 star general). At the end, I'm not gonna ruin anything, but manly tears will be shed simply because of how much of a hero Capitan America truly is.