Maria Hill is the modern MCU's answer to Peggy Carter - a powerful S.H.I.E.L.D agent who keeps the good fight going when everyone around her is failing. Hill first appeared in The Avengers and has since had more time to grow into her role as a recurring character on Agents Of S.H.I.E.L.D. Across all of her appearances, Cobie Smulders has been consistently extremely cool and level-headed as the world around her descends into chaos. One of the underlying stories in the Marvel universe is that S.H.I.E.L.D director Nick Fury (Samuel L. Jackson) can be kind of reckless as a leader (something which is usually forgiven because he's also powerful and charismatic), thus given an added sense that the organisation would have collapsed without Hill as his deputy. Fortunately, she's now working directly with The Avengers, so her role looks set to grown even more.