During Tom King's run, the heroes found out that Eobard Thawne had placed Thomas on Prime Earth so he had to watch his son live out the same brutal life as a vigilante that Thomas had.

Source: https://www.cbr.com/thomas-wayne-batman-before-flashpoint-dc-comics/

Feeling he lost too much, Flash traveled back in time to capture Eobard Thawne before he killed his mother, Nora Allen.

Source: https://www.cbr.com/flash-flashpoint-alternate-versions-dc-comics-tv-movies/

Once the biggest fan of the Flash, Thawne has made it his life's mission to make Barry's life a living hell.

Source: https://screenrant.com/flash-reverse-knight-terrors-gorilla-grodd/

The scene held an ominous tone, with Iris noting that the Negative Speed Force was bound to choose a new avatar to replace Thawne and counter Barry.

Source: https://screenrant.com/the-flash-season-9-unanswered-questions-mysteries/

Tom's exciting portrayal of Eobard Thawne has been unforgettable for nine years and fans will be delighted to know that he's brought that same wonderful intensity to our finale, too."

Source: https://comicbook.com/dc/news/the-flash-tom-cavanagh-always-knew-series-finale-return-reverse-flash/