I don't know if this is the first or not (under the traditional definition of civilian), but I don't think your link is not a counter example... Sergei Propopy

I don't know if this is the first or not (under the traditional definition of civilian), but I don't think your link is not a counter example... Sergei Propopyev apparently commanded that mission, and per NSF immediately before becoming a cosmonaut he was the commander of an aviation group of strategic bombers with the 121st Heavy Bomber Aviation Regiment in the Saratov region. https://www.nasaspaceflight.com/2018/06/soyuz-ms-09-crew-artificial-intelligence-launch-station/ https://www.nasaspaceflight.com/2018/06/soyuz-ms-09-crew-art...