Brian Thomas Smith As Zack Johnson
Zack Johnson is a recurring character in Big Bang Theory who first appears in season three. He is portrayed as a friendly but dim-witted individual with a heart of gold. Zack is introduced as Penny’s ex-boyfriend and becomes a love interest for her once again in later seasons. Despite his lack of intelligence, Zack is depicted as a kind-hearted and good-natured person, always willing to help others, particularly his friends Leonard and Penny. However, his naivete often leads him into humorous situations, such as when he believes that the LHC (Large Hadron Collider) is a new type of drink.