Who Plays Zack On The Big Bang Theory & What Happened To Him?

Before Penny (Kaley Cuoco) ends up with Leonard (Johnny Galecki) on "The Big Bang Theory," much is made of her unsavory dating history. "You're the first guy [my dad's] ever really approved of, you know?" she tells Leonard in Season 4. "You're a scientist who went to college, and you don't have a neck tattoo, or outstanding warrants, or a baby."

Penny's love interest, Zack, played by Brian Thomas Smith, is certainly no scientist; the guys imply he is dumber than a dolphin. But he also isn't a philandering jerk, unlike some of Penny's former beaus. Smith made his first appearance as Zack in the Season 3 finale.

"I had never seen an episode of the show, not many people had," Smith recalled to VoyageLA. "I was only supposed to do one episode, but the producers really liked the way I played the lovable, dim-witted Zack and kept bringing me back for some really funny episodes over the next nine seasons. It's cool getting recognized for my role on that show by fans."

Smith plays Zack on 11 episodes, and the writers clearly had fun with the character. In Season 7, Zack and Penny annul their accidental marriage, officiated by an Elvis impersonator in Las Vegas a few years prior. In Season 12, Zack and his similarly dim-witted wife approach Leonard to be their surrogate father.

Following "The Big Bang Theory," Smith secured more guest roles on shows like "9-1-1: Lone Star" and "NCIS." He also appeared on "United States of Al."

Brian Thomas Smith first appeared in a Chuck Lorre show in 2006, playing Emmett on an episode of "Two and a Half Men." His performance as Zack on "The Big Bang Theory" must have stuck with the prolific showrunner because Smith was cast as Freddy in the Lorre-produced "United States of Al."

"United States of Al" premiered on CBS in 2021 and follows the friendship between Marine veteran Riley (Parker Young) and his Afghan interpreter, Al (Adhir Kalyan), as they settle in Ohio. There, Riley reconnects with his daughter, Hazel (Farrah Mackenzie), and his estranged wife, Vanessa (Kelli Goss). Freddy is Vanessa's goofy, well-meaning boyfriend with a passion for magic.

Smith joined the series halfway through Season 1, so he was thrilled to have an even bigger role when the show was renewed for a 2nd season. "David [Goetsch] and Maria [Ferrari], who created the show with Chuck Lorre, they brought me in around Episode 6," the actor said on the "Traversing the Stars" podcast. "They got the news that there was a Season 2, and it was so cool because they ended up using me [for] 11 out of 22 episodes. As a recurring actor, that's pretty cool. Especially with the way it went down on 'The Big Bang Theory.' [They used] Zack once or twice a season for nine seasons."

"United States of Al" was canceled after two seasons, but Smith has stayed busy. He landed roles on episodes of Nickelodeon's "The Really Loud House" and the Christmas movie "Holiday Twist."