Corrupt Counterparts of the Fastest Men Alive

Eobard Thawne and Professor Edward Clariss, as previously mentioned, used their considerable intellect to artificially reproduce the superspeed manifested by their hated obsession, the Flash of Two Worlds. Their motivation being greed for ill-gotten gains was exceeded in Thawne's case by his lust for Iris West, the wife of Barry "Flash" Allen. 

Thawne adopted various aliases during his criminal career throughout the years. Not only did these include the Reverse Flash, but also Professor Adrian Zoom. On at least one occasion, Eobard even assumed the alter ego of the Flash himself, after temporarily ensnaring Barry Allen in a seemingly inescapable trap. Interestingly, there is evidence that Clariss also had another alter ego, prior to his appearance as the Rival.

By the time Clariss had encountered Jay "Flash" Garrick's girlfriend Joan Williams, he was of to advanced an age to notice her at that point. However, in the years leading up to his return to Keystone City, during the early 1940s Edward stated he moved to Europe to pursue his superspeed research. Feeling disenfranchised with the United States, whose scientists scoffed at his scientific theories, the German government would've supported for his passion project.

Siegfried the Speedster aka Zyklon appeared in early 1942 working alongside Baron Blitzkrieg, and battled the Flash and Johnny Quick on one occasion. When he disappeared by 1943, the Flash assumed the Siegfried alter ego in a scheme to assist his Justice Society teammate Wonder Woman. So one may ask, are Zyklon and Rival one and the same*?

Just like Clariss, Thawne had a propensity to assume other identities to disguise his amoral agenda. Among these aliases Sorban, when Zoom pretended to be the alien Venturian gambler. Zoom along with a fake version of that Sorban’s partner Rokk fabricated a race involving Flash and Superman (Rokk was in reality another foe of the Flash, Abra Kadabra, and the pair were revealed following the conclusion of the heroes' race).

When Zyklon's superspeed was shown to be second best to America's twin speedsters, the Flash and Johnny Quick, apparently Clariss was encouraged to devote his time to other scientific pursuits. This left him bitter and disenfranchised, motivating him to resume a costumed career, as a mirror image of the original Flash. Which is ironic, since the Flash became a mirror image of Zyklon years earlier when he briefly became Siegfried the Speedster.

* While Zyklon spoke in a German accent including using distinct Germanic vocabulary, undoubtedly Zoom likewise mimicked the vocal cadence of Sorban's alien dialect.