Despite being killed off in The Flash season 1, Reverse-Flash always finds a way to return to Central City to renew his rivalry with the Scarlet Speedster. The evil villain known for murdering the Flash’s mother considers himself to be Barry Allen’s (Grant Gustin) greatest enemy. Though Barry thought he was done with Eobard Thawne at the end of season 1, the threat he poses to Barry and Team Flash persists even now.
After discovering the person who murdered his mother and framed his father for her death was the Reverse-Flash, Barry and his team became focused on defeating him. As the season progressed, the truth about Reverse-Flash’s real identity came to light; as it turned out, Eobard Thawne (whose real persona is played by Matt Letscher) came to the present years ago and replaced Harrison Wells (Tom Cavanagh). After a long struggle, their plan to beat Reverse-Flash fell apart in the season finale, forcing his descendant, Eddie Thawne (Rick Cosnett), to take matters into his owns hands. Eddie killed himself to keep Eobard from ever being born. As a result, Eobard was erased from existence.
Though this turn of events made it seem that Eobard was gone for good, the Arrowverse has brought him back on more than one occasion. It’s important to keep in mind that there isn’t any one explanation for why Eobard never stays gone for long. The first time he was brought back was a result of the creation of the Flashpoint timeline in season 3. The version of Reverse-Flash that battled the crew of the Waverider in Legends of Tomorrow season 2 wasn’t the real Eobard Thawne; he was actually Eobard’s time remnant. He was created when Barry changed the past by stopping Thawne from killing his mother.
Reverse-Flash returned again in the Crisis on Earth-X crossover event. This incarnation of the character was revealed to be the Reverse-Flash of an alternate timeline, which means that he’s technically different from the villain that was erased by Eddie in season 1. It’s been stated that the Crisis on Earth-X Reverse-Flash is the one that was imprisoned in the future in The Flash season 5. He’s also the same character that merged with all other versions of Harrison Wells into Nash Wells. He attempted to make a complete return by taking possession of Nash, but his scheme was thwarted by Team Flash.
He was “exorcised” from Nash’s body, but that doesn’t mean he’s gone forever. The Flash season 7 is likely to resurrect him - and the series has already explained how it will happen. The show laid the groundwork for another Reverse-Flash revival by mentioning that, though Eobard doesn’t have a body, he can get a new one by taking over someone else’s. The original The Flash season 6 finale was supposed to lead into his return, but a shortened season kept this from happening. What all this means is that in season 7, Reverse-Flash may return looking like someone else.