The Flash season 5's villain, Cicada, might be from the future. This would represent a major change from the character's origins from the comic books and be one of several things that have been changed in adapting Cicada for the Arrowverse.
Created by writer Geoff Johns and artist Scott Kolins, Cicada first appeared in The Flash (Vol. 2) #170 in March 2001. Cicada was originally an Old West preacher named David Hersch, who murdered his wife and was struck by lightning as he was about to commit suicide in a moment of regret. The lightning transformed Hersch into a vampire of sorts, who could drain the life force from other people in the form of lightning, extending his own life for over a century. Hersch believed that The Flash had been empowered by the same lightning and formed a cult which began sacrificing people whom The Flash had saved, in a bid to resurrect Hersch's wife.
Little has been said precisely about how Cicada would differ from his comic book counterpart on The Flash beyond his targets and powers changing. A casting breakdown originally described the main villain of The Flash's season 5 as a man named Desmond Paul, who was semi-immortal and blamed other metahumans for his suffering. The breakdown also said that Paul would have the ability to negate the powers of other metahumans. It was later confirmed that Desmond Paul was Cicada and that he would be played by actor Chris Klein.
The second episode of The Flash season 5, "Blocked", largely centered around Team Flash's efforts to stop Block - a metahuman gun-runner with the power to create blocks of solidified air. Once Block was subdued, Cicada emerged and attempted to kill her with one of his trademark lightning-shaped daggers. It was here that it was confirmed that the television version of Cicada could neutralize another metahuman's powers, as Cicada was able to face a depowered Flash, Vibe and Elongated Man with ease. Indeed, Cicada would have killed The Flash had it not been for the timely arrival of XS, Barry's speedster daughter from the future.
For some reason, the sight of XS and her calling out "Dad!" as Cicada was about to stab The Flash made the villain stop in mid-strike. He then stood up and walked away before anyone could stop him. Why he did so is anyone's guess at this point, but it is clear that Cicada recognized XS somehow. The most likely explanation for this is that Cicada is another time-traveler but as countless episodes of The Flash have proven in the past, the most likely explanation isn't always the correct one.