Natalie dormer is one of the front runner to play Captian marvel, how ever she has appeared in the marvel universe before. It's not like marvel to ignore something like that so here is my theory of how that role could fit in. The role In question is from Captian America the first avenger where she as an unnamed woman kisses Steve Rogers. Spoilers if you are not catch up on agent of shield. We have found out that a blue alien was kidnapped by hydra and then shield. We have found out that this alien was in fact a kree. We will assume you know what a kree is. What if that was the first Captian marvel or Mar'vel as he is named in the comics. A super kree who's mission it was to find an infinity gem which the red skull has at this point. Coming for a war with the skralls or xandoreins (which ever they would have been at war with) but at the same time being a good man, he works with the same group that make Captian America then meets and falls in love with the young lady below. Before he is taken by hydra he some how gives his powers which includes immorality. She would the spent years and years changing her name until the avengers show up. At the time of the battle of new York she would be on her way to help but by the time she gets there everything would be over. Then later she finds captain America and is one of the new people has gets together for his new avengers in civil war. Cap would need some raw power cuz iron man will have the hulk cuz of science bros and Thor might side with him as well. Maybe this is bull but I like to think maybe.
Now how did I get immortal out of this set up? Captian Mar'vel may have been immortal. It's reaching I know but still Hear me out. His body didn't looks like it aged in present day and he was around since the 50's or so. We know one inhuman was immortal and the inhumane are related to the kree. This would connect not only the first avenger but agent's of shield as well.