Brian Thomas Smith (born May 13, 1977) is an American actor and comedian known for playing the dim-witted but kind-hearted Zack Johnson in The Big Bang Theory for nine seasons.

He has also made other TV appearances on Fear Factor, Two and a Half Men, Happy Endings, The Neighborhood, 9-1-1: Lone Star, and United States of Al. On the big screen, Smith starred opposite Al Pacino and Annette Bening in Dan Fogelman's directoral debut film, Danny Collins.

[citation needed] Smith has appeared in over 100 commercials including Miller Lite, Pizza Hut, Burger King, State Farm, Lopez Tonight, Chevrolet, Carl's Jr., Coors Light, Budweiser, Taco Bell, DirecTV, Pop Chips, Buffalo Wild Wings, Honda, Corona, Applebee's, DairyQueen, Audi, and Progressive Insurance.

[citation needed] In 2010, Smith joined the cast of comedy series The Big Bang Theory in a recurring role, portraying Penny's sometime boyfriend, sometime ex-boyfriend, Zack Johnson.

In 2021, Smith was cast in a recurring role of the comedy series United States of Al, as Freddy, the new boyfriend of Vanessa, Riley's ex-wife.