Big Bang Theory Stars Before They Were Famous: See Their Surprising Early Roles
Johnny Galecki: Then
Before finding his inner geek on The Big Bang Theory, Galecki was best known for playing David Healy on Roseanne. But he also had roles in some other 1980s and '90s classics. In 1989, at age 14, he starred as Rusty Griswold in National Lampoon's Christmas Vacation, alongside Chevy Chase, Beverly D'Angelo, and Juliette Lewis.