'DC's Legends of Tomorrow' will add two new characters before season 1 ends. Arrow's Ra's al Ghul will make his debut as the 1950's leader of the League of Assassins during 'Legends of Tomorrow' episode 9, "Left Behind," when White Canary decides to rejoin. Another superhero will also be introduced in the 'Legends of Tomorrow' season finale, possibly Rip Hunter's friend Booster Gold.