Warning: spoilers ahead for The Flash #761!
The Reverse-Flash has just confirmed that he is the greatest of all The Flash's villains, and quite possibly the greatest villain in the DC Universe. Apparently, killing Barry Allen's mother was just the beginning of a master plan orchestrated by Eobard Thawne to ensure that the lives of Barry and his family would be fraught with pain and suffering. In Joshua Williamson's Flash #761, the scope of Thawne's plan is revealed, and it may be more than the Flash can bear.
In the finale arc of writer Joshua Williamson's run on The Flash, the Flash initially has the odds stacked against him thanks to the work of the Reverse-Flash. At first, the Reverse-Flash's plan was to possess Barry's body while trapping his mind within a Speed Force limbo. He was aided by Gorilla Grodd, the Turtle, Captain Cold, the Trickster, and even the Tornado Twins - future versions of Barry's children - all of whom he had pulled from different points in time to serve as his Legion of Zoom. However, Barry received help from his Flash Family, breaking free of Thawne's control (while also rescuing Max Mercury and Jesse Quick from the Speed Force limbo). This was only the first act of Thawne's plan however, as he then gathered his entire Legion of Zoom, consisting of nearly every villain and rogue the Flash Family has ever faced. Max Mercury summoned even more Flash Family members from across time to assist in the fight, and thus began the biggest battle in Flash history.
As the battle threatened to destroy Central City, Thawne revealed a master plan that has taken him years of meticulous planning and preparation. Not only was he instrumental in the creation of other rogue speedsters such as Zoom and Godspeed, but he also used the Negative Speed Force in a way that Barry never thought possible, giving Thawne a terrible power he's used several times over the course of the Flash Family's lives without the Flash ever having realized it.
Using a hypnotic frequency accessible through the Negative Speed Force, Thawne was able to shape events and actions as he saw fit, acting as a negative guiding force in the lowest moments of the Flash Family. Barry is shocked and angered as Reverse-Flash reveals he encouraged them to make the same mistakes again and again, all to shape a future where he's the one and only celebrity speedster. After hearing this, the Flash seems ready to kill Thawne for what he's done, and he chases the Reverse-Flash with a vengeance. While the younger members of the Flash Family are able to transport everyone back to their original timelines and save the city, their work has no effect on Thawne and Barry, who are racing within the timestream itself.
After this major reveal that Thawne has been responsible for causing so much of the pain the Flash Family has endured over the years, it's safe to say the Reverse-Flash isn't just the greatest Flash villain of all time, but also in the DC Universe as a whole.