Cause Of Death: Killed by Oliver Queen in a swordfight during the Season 3 finale. Why It's Important: For a start, killing Ra's allows Oliver and the rest of Team Arrow to successfully save Starling City. It also completes the arc of Oliver pretending to be loyal to the League of Assassins, blowing his cover once and for all to give a satisfying conclusion to something that had perhaps been a bit of a misstep in the first place. In terms of wider importance to the show, this allowed the series to lift the veil of darkness that hung over the show during the third season, prompting Oliver to want to become a happier person, thus leading to his relationship with Felicity and his becoming the Green Arrow.