WARNING: This article contains major spoilers for Season 6 of The Flash.
Like clockwork, Eobard Thawne, the fearsome Reverse-Flash, has resurfaced across every single season of The Flash to menace Barry Allen and his friends and family. In a way, this makes a great deal of sense: The Reverse-Flash is the Scarlet Speedster's greatest, most personal foe. He traveled back in time to brutally murder Barry's mother and frame his father for the crime. And, in the Arrowverse, Thawne caused the S.T.A.R. Labs particle accelerator explosion that transformed Barry into the Flash in the first place, a move that was the speedy villain's desperate attempt to return to his own time in the far-future.
However, after the villain's most recent appearance in the show's sixth season, in which he threatened Team Flash once again by temporarily taking control of Nash Wells' body, it is probably best for the character to remain trapped in his Negative Speed Force until the series reaches its eventual conclusion. This would prevent audiences from taking the Reverse-Flash for granted while setting up a truly epic rematch between the two speedsters before the popular Arrowverse series signs off for good.
Serving as the primary antagonist for The Flash Season 1, Thawne had resurfaced briefly in sequences set in the past in subsequent seasons as well as serving as the main antagonist in Legends of Tomorrow Season 2 after Barry set Thawne free in The Flash's third season premiere. In Season 4, Thawne appeared on Earth-X during the Arrowverse's annual crossover, while Season 5 revealed Thawne as the secret mentor to Barry's adult daughter from the future, Nora. Now, following the reality-altering events of "Crisis on Infinite Earths," Eobard Thawne is still alive and well, existing within his own self-created Negative Speed Force.
After Season 3, The Flash expanded Barry's primary, seasonal antagonists so they were more than rival speedsters. Season 4 had Team Flash taking on the Thinker, in Season 5 the team went up against the murderous Cicada and, in the first half of Season 6, the heroes faced Bloodwork, with a new Mirror Master emerging as the big bad in the season's second half. Bringing Reverse-Flash back before the end of the series distracts from whomever else Team Flash is facing. It also stands the chance of demystifying Thawne himself. The less we see and know about the futuristic villain, the better.
And bringing back Reverse-Flash as a final season villain would create a poetic parallel to the DCTV series' first: It was Thawne who ironically made Barry a superhero in the first place, and his murderous legacy has weighed heavily over the team ever since. And if the show ever decides to return to having a rival speedster as a future overarching antagonist, there is no better choice than the Reverse-Flash -- but this is best saved for the show's end as an earlier return would feel anticlimactic.
With Eobard Thawne trapped in the Negative Speed Force instead of eliminated outright, it is only a matter of time before he breaks free and confronts Barry once again. There is no set end date for The Flash at this time, though star Grant Gustin's contract is up for renewal following the upcoming seventh season. Should the Arrowverse series come to an end following this, a return of Eobard Thawne would be the perfect way to send the show off as the Flash and the Reverse-Flash have their definitive final showdown.
Airing Tuesdays at 8 p.m. ET/CT on The CW, The Flash stars Grant Gustin, Candice Patton, Carlos Valdes, Danielle Panabaker, Tom Cavanagh, Jesse L. Martin, Danielle Nicolet and Hartley Sawyer.