Complex sentence: A former S.H.I.E.L.D. agent by the name of Mainspring was heading a project called the Gatekeepers, whose goal is to study and destroy Phalanx technology.
Split into simpler sentences: A former S.H.I.E.L.D. agent by the name of Mainspring was heading a project called the Gatekeepers. Their goal was to study and destroy Phalanx technology.