The Arrowverse has seen some formidable villains. Bad guys like Damien Darhk, Zoom, Savitar, and Vandal Savage have all proven to be difficult for the heroes to defeat and even when the good guys prevail, there are always more villains to face. However, now that "Crisis on Earth-X" has concluded and the world saved from Nazi invaders it's pretty clear who the most powerful Arrowverse villain we've seen yet is -- Eobard Thawne.
While there are villains who have been physically harder to defeat, such as the functionally immortal Vandal Savage on Legends of Tomorrow and the nearly untouchable due to dark magic Damien Darhk on Arrow before becoming an evil fixture on Legends and villains difficult to get ahead of, such as The Flash's big bad this year, The Thinker, there are few villains who have been able to accomplish as much chaos across not just the Arrowverse, but time and the multiverse itself as Eobard Thawne has. Thawne has somehow managed to come back from being completely erased from existence at the end of The Flash's first season to somehow travel to Earth-X and help them invade Earth-1. That's pretty powerful, but it's not just the big example that makes Thawne the most powerful villain. For Thawne, it's all about the details, which is why we're breaking down exactly what makes him the biggest bad in the Arrowverse.
Metahumans are all his fault
One of the biggest threats in the Arrowverse are metahumans. The particle accelerator explosion that gave Barry Allen (Grant Gustin,) Cisco Ramon (Carlos Valdes,) and Caitlin Snow (Danielle Panabaker) their superpowers also gave abilities to a whole lot of other people who are less inclined to use those powers as a force of good. In fact, that's largely the premise of The Flash each week: the team discovers a new metahuman causing problems or hurting people in Central City. This season, they're dealing with a new crop of metahumans that, while created by Barry's return from the Speed Force, are largely the products of the machinations of one of those original metahumans. That's a lot of chaos and the responsibility for that can be placed at the feet of one man -- Eobard Thawne.
During the first season of The Flash it was revealed that Thawne, who originally hails from the 22nd century, travelled to the 21st century and set in motion the events that not only lead Barry Allen to becoming The Flash, but was also responsible (while posing as Harrison Wells) for the particle accelerator disaster that gave Barry and countless others their powers. The Thinker only created a dozen metas on a bus. Damien Darhk only managed to nuke a city. Vandal Savage got thwarted. Even if Thawne was fully defeated tomorrow, he has still given the Arrowverse enough problems to last a lifetime.
Death can't stop him
At the end of The Flash's first season it looked like, while the metahumans would live on, the road had come to an end for Thawne. Before Thawne could kill Barry and return to his own time, Thawne's ancestor, Eddie (Rick Cosnett) kills himself, causing Thawne to never have existed. The act saves Barry and appears to end Thawne as well as create a black hole over Central City. The heroes do manage to save the city and close the black hole in the second season, but Thawne shows up again, this time from a point in the future before he had originally come back to kill Barry's mom, thus protecting that version of Thawne from being erased from existence and revealing a curious loophole in how time works with speedsters: Time Remnants.
Created as a result of speedster time travels, time remnants are created by the various timeline ruptures and changes time travel creates so the Speed Force keeps those duplicates as parts of their original timelines to prevent issues with time paradoxes. This is a Speed Force feature that Thawne uses multiple times in order to evade death. Erased from existence? No worries, a Thawne still exists to keep the timeline stable and that version can go on to cause trouble. In fact, it's a time remnant version of Thawne who is able to go back in time to pull a version of Damien Darhk from before his death on Arrow to help him form the Legion of Doom and quest for the Spear of Destiny that would allow Thawne to rewrite time itself.
The Legion of Doom
About that whole getting the Spear of Destiny and rewriting time and reality. Why would Thawne need to rewrite time and reality? Well, there is a slight problem with time remnants. The Speed Force doesn't like them running around causing problems and will hunt them down. During the second season of Legends of Tomorrow, Thawne is being chased by the Speed Force's Black Flash enforcer and the only thing that can stop Thawne from eventually being caught and dealt with is the spear. With it, Thawne can create a reality built to his desires and whims. But he can't do it alone, which is why Thawne puts together a team that would be similarly interested in creating their own reality. This leads him to pull Damien Darhk from a time before his death, and join forces with Malcom Merlyn to get that spear.
And they do get the spear. And they do create their perfect reality. But their victory is short-lived. The Legends manage to go back in time and stop Thawne -- who summoned an army of his own time remnants -- from using the spear. For the first time the wicked speedster wasn't fast enough and ends up being killed by the Black Flash enforcer along with all of his time remnants, but even that has long-lasting impacts. Because the Legends were forced to interact with their past selves in order to stop Thawne, they might have broken history and time themselves as seen when they arrive in Los Angeles in the present day only to encounter dinosaurs in the streets.
He continues to have control over Barry
Despite Barry defeating Thawne more than a few times, Thawne continues to have control over Barry and, in fact, has even made the hero a participant in the defining trauma of his life. How did he manage that? Well, it's because of a little thing called Flashpoint. After the death of his father, Henry Allen (John Wesley Shipp,) at the hands of Zoom, a devastated Barry decides to race back into the past and save his mother by stopping Thawne from killing her. He also brings Thawne back with him to the present and keeps him locked up to prevent anything further from happening. Unfortunately, the Flashpoint timeline may be great for Barry but is horrible for those he loves. Barry is thus forced to take Thawne back to the past, so Thawne can kill Barry's mom to reset the timeline.
Think of it this way: Barry facilitated his own mother's murder by bringing her killer back to the right place and the right time. Add to that the metas created when Thawne sparked the particle accelerator disaster, particularly The Thinker, who might be the most dangerous meta Barry has faced yet, and Thawne's influence over Barry's life never, ever stops.
While we don't exactly know how Thawne managed to go from being erased by the Speed Force during the Legends of Tomorrow season to conspiring with Nazis on Earth-X during this season's crossover, it's made pretty clear that the Wells' face wearing Thawne is, in fact, the same nemesis Barry has been dealing with since season one. Now he's just no longer content to bounce around time to reach his end goal of destroying Barry. He's willing to jump the multiverse, too. What Thawne's end goal with the Earth-X Nazis was specifically remains unclear, but whatever his goal was it clearly included tormenting Barry Allen. When The Flash manages to get Thawne in a position where he could kill him and, in theory, end it all, Barry is unable to, leading Thawne to taunt Barry. "I wonder what face I'll be wearing next time we meet, Flash," Thawne says before speeding off and we will no doubt be meeting this powerful villain again.
The Flash airs Tuesdays at 8/7c on The CW.