 Casting reached its final stages the following year . In February 2011 , Cobie Smulders acquired the role of Maria Hill , after participating in screen tests conducted by Marvel for the role of a key S.H.I.E.L.D. member , who Samuel L. Jackson described as Nick Fury 's sidekick . Over the successive months , the film 's cast expanded to include Stellan Skarsgård , Paul Bettany , and Gwyneth Paltrow . Paltrow was cast at Downey 's insistence ; prior to this , Whedon had not intended the film to include supporting characters from the heroes ' individual films , commenting , " You need to separate the characters from their support systems in order to create the isolation you need for a team . " 
