While the Flash has faced many villains on his self-titled show, none can compare to Eobard Thawne, who has inflicted by far the most trauma of any big bad on Barry Allen's life. First presented as a speedster from the future with an unhealthy obsession with Barry, fans have learned more about the Flash's greatest enemy in each of his subsequent appearances. After his return once again in The Flash episode, "Death of the Speed Force," it seems there is more to be revealed about Thawne's origin and the source of his powers.

Since the events of "Crisis on Infinite Earths," Barry has been dealing with all the ways things have changed, and he learns the Speed Force is dying. For Barry, this death is a terrible loss that ensures he has a limited amount of time before he completely loses his powers. Just as Barry learns about the Speed Force's demise, however, Thawne returns to gloat that the death of the Speed Force is no problem for him because, as he reminds Barry, "I built my own."

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The force Thawne made, the so-called Negative Speed Force, is both separate from and connected to the original Speed Force. As Barry developed his relationship with the Speed Force, Thawne realized that he needed a force that was wholly his own so there was no possibility that it could be taken from him. This new force was merely a corrupted version of the Speed Force. While it can stand alone, its connection to the Speed Force allows it to become stronger when the user has access to both forces. With the Speed Force dead and its energy slowly dwindling, Thawne's creation will allow him to keep his speed and remain Barry's most formidable enemy.

In the comics, Thawne uses himself as the generator and originator of the Negative Speed Force. This means that his use of its speed only adds to the overall power of the Negative Speed Force. This version of the Negative Speed Force works as an infection that can impact any speedster that comes into contact with it. During a battle shown in Joshua Williamson and Carmine Di Giandomenico's The Flash run, Barry was infected by the Negative Speed Force after defeating Thawne. Although he never made the choice to access this force, Thawne put Barry into contact with it. From there, Barry was forced to deal with the many negative consequences that come from this source of power.

These consequences primarily affect the personality of the force's users. As Barry continued to maintain his connection to the Negative Speed Force, he became more prone to rage and quicker to violence as all of the hate and darker thoughts he had were pushed to the top. Beyond this the Negative Speed Force can also become extremely destructive when it's use. While the regular Speed Force produces harmless lightning when a speedster uses it, Barry found black lightning emerged from him when he used the Negative Speed Force, and this lightning destroyed anything that came into contact with it. At this point, these side effects have only briefly been hinted at on the show.

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CW The Flash, Grant Gustin promo poster

During the previous season of The Flash, Nora West-Allen accessed the Negative Speed Force by using all the negative emotions she already felt. However, Nora learned that the force would send her down a dark path when she used it so she ultimately decided against accessing it further. If Barry is infected by it or makes the decision to access it, viewers will see the effects this force has on the titular hero.

Going forward, Barry and his allies will have to prepare for a world with no Speed Force. Although they have some ideas about what to do, they have to reckon with the fact that Thawne is patiently waiting for his time to strike, safe from the potential loss of his powers -- something that makes him more dangerous than ever. As Team Flash learns more about Thawne's Negative Speed Force, its deadly nature will only become more evident.

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.

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