Rise to Fame
The breakthrough came later than expected and by a strange route. He spent years doing improv at Second City in Chicago under Del Close, then grinding through TV guest spots (ER, Gilmore Girls, How I Met Your Mother) before landing a cult role as the sleazy writer Paulie G. in HBO's The Comeback (2005) opposite Lisa Kudrow. It's Always Sunny in Philadelphia gave him another recurring villain credit. None of it was a star turn. Then Young Sheldon landed, and George Cooper Sr. turned out to be the role he'd been quietly training for his entire career.
In the Spotlight
The George Cooper role came with a built-in contradiction: adult Sheldon spent 12 seasons on The Big Bang Theory describing his dad as a womanizer who cheated on his wife, and Young Sheldon quietly turned George into the warmest person in the room. Barber played the retcon straight for all seven seasons. George died of a heart attack offscreen in Season 7, but the character didn't stay dead long. Barber is now doing dream-sequence cameos in the spinoff Georgie and Mandy's First Marriage, because apparently the franchise isn't finished with George Cooper yet.
Side Notes
His father, an Army MP, was killed in the line of duty when Barber was one year old. He doesn't lead with that publicly. What he does talk about is the improv pipeline: Second City under Del Close in Chicago, alongside a pre-famous Jack McBrayer, and early stage work at Michigan's Barn Theatre alongside a pre-famous Jennifer Garner. Playing Leonard's high school bully in a 2011 Big Bang Theory episode, years before being cast as George Cooper, means he technically haunted the same franchise twice.