Mengele

"Mitts off, Mengele."

- Ray Palmer comparing Eobard Thawne to Mengele

Mengele was a Nazi doctor on Earth One.

Biography
At some point Mengele had become a notorious Nazi scientist on Earth One known for human experimentations.

Ray Palmer compared Eobard Thawne to Mengele as the latter was a Nazi party member on Earth-X at the time, dressed in a medical garb as he was about to dissect Kara Danvers to extract her heart for her Earth-X doppelgänger to transplant.

Behind the scenes

 * In the real world Josef Mengele was a member of Schutzstaffel and a medical doctor notorious for conducting human experimentations in concentration camps.
 * Eobard Thawne's surgical garb which drawn comparison to Mengele is indeed similar to how Mengele often depicted in popular culture.