2. Peggy Carter (Marvel Cinematic Universe)
Peggy Carter appeared in Captain America: The First Avenger as an officer of the British Armed Forces before and during World War II. As an agent of the Special Air Service, she joined the Strategic Scientific Reserve (SSR), an Allied deep science agency formed to fight against HYDRA - the Nazi super weapons division - which was chiefly involved in the development of the Super Soldier Serum that would ultimately be given to Steve Rogers. During the war, she met and fell in love with Steve Rogers - the two having planned a date prior to his apparent demise in a plane crash following on from his fight with the Red Skull. She would go on to join S.H.I.E.L.D. The on-screen chemistry and relationship between Carter and Rogers was one of the few in superhero movies that we actually wanted to see more of, so it was a shame that Rogers was taken out of her life so abruptly and quickly. Further on-screen development of that relationship would have been welcomed with open arms. It would also have been good to have seen her as an elderly lady in the Avengers, but she was barely mentioned. Hopefully, this is one situation that will be rectified somewhat in both flashback scenes and modern scenes in Captain America: The Winter Soldier, which comes out next year.