The character Atwell will play is named Peggy Carter, who in comics lore not only dated Captain America but was an agent helping the French Resistance. She later became the aunt of Sharon Carter, Captain America’s love in modern times.
Seems Atwell won the role last week after her screen test in London. Other actresses that were considered for the role of Peggy Carter were Keira Knightley and Emily Blunt.
Hayley Atwell would be better known in the US for her role of Bess Foster in the movie The Duchess. She played the Duke's (Ralph Fiennes) mistress.
Atwell is a good actress so I'm hoping the role will suit her or vice-versa and I really, really hope that she and Chris Evans will have good chemistry.