Brian Thomas Smith is an American actor and comedian best known for his recurring role as Zack Johnson on The Big Bang Theory.

Smith first appeared on television in 2003 as a contestant in an episode of Fear Factor and, in 2005, competed with his brother Greg on The Amazing Race 7.

His first television acting credit came with a 2006 episode of Chuck Lorre's Two and a Half Men. His other early credits include A Good Knight's Quest, Casual: The Series, Wolfpack of Reseda and Happy Endings.

Smith first appeared on The Big Bang Theory in 2010 as Zack, Penny’s good-natured but not particularly bright ex-boyfriend. He went on to make recurring appearances through the show’s final season.

His later television credits include guest appearances on The Neighborhood, 9-1-1: Lone Star, NCIS and Shrinking, along with a recurring role on Bad Monkey. He also played Freddy on Chuck Lorre’s United States of Al.

On film, Smith appeared in Danny Collins, starring Al Pacino and Annette Bening. His other film credits include Lethal Seduction, Babysplitters and Holiday Twist.