While Arrow and The Flash have done exemplary jobs of telling the stories of their respective heroes, the upcoming DC's Legends of Tomorrow seems poised to truly tie the entire Arrow-verse together as a cohesive, connected world. While the heroes that comprise the show's team come from all avenues of the universe (Captain Cold, Hawkgirl/Hawkman, and so forth), so too will the villains.
While Vandal Savage (Casper Crump) will represent the overarching villainous threat on Legends of Tomorrow season 1, he will be far from the only familiar enemy encountered by the show's ensemble of misfit heroes. We now know that a familiar threat from Arrow will once again rear his head; the Demon's Head to be more precise.
CB reports that actor Matt Nable will return to the Arrow-verse to once again terrorize civilization as ancient warrior Ra's al Ghul in Legends of Tomorrow. As fans of Arrow already know, Ra's' plan to destroy Starling City was foiled last season due to intervention by Team Arrow. The season finale ended with Ra's' apparent demise at the hands of Oliver Queen, leaving the world short one iconic DC villain.
Given the time travel element of Legends of Tomorrow, it remains unclear if the appearance of Ra's al Ghul will take place before or after the events of Arrow's third season. CB has also reported that Damien Darhk (Neal McDonough) will appear on Legends, so a story arc chronicling the tumultuous past relationship between these two villains seems entirely plausible. Then again, this is The CW we're talking about, so resurrection of any previously deceased characters does not seem entirely off the table.
The implications of Ra's' return seem likely to have the most profound effect on White Canary AKA Sara Lance (Caity Lotz). Following her recent dip into the Lazarus Pit on this season of Arrow, she has experienced violent mood swings and a dangerous blood lust character. Given her prior relationship with Nyssa al Ghul, and her dark, violent past with Ra's' League of Assassins, it would seem likely that she will not have the most jovial response when she encounters the centuries old assassin.
The Flash will return on Tuesday, January 19, 2016, while Arrow will return on Wednesday, January 20, 2016 and Legends of Tomorrow will see its series premiere on Thursday, January 21, 2016.