'Big Bang Theory' Star Johnny Galecki Played Rusty in the 1989 Classic Chevy Chase Flick 'Christmas Vacation'

Dr. Leonard Hofstadter (played by Johnny Galecki) got his first real big break in the classic National Lampoon's Christmas Vacation film with Chevy Chase as Rusty Griswold.

With the Christmas season just beginning and the networks playing around-the-clock Christmas movies, fans of Big Bang Theory are sure to recognize Leonard as the son of clumsy Clark Griswold (Chevy Chase).

The 39-year-old actor was just 14 when the classic holiday movie came out as he acted alongside his TV dad Clark Griswold and ventured out into their famous family station wagon to pick out a tree, but forgot to bring an axe or a saw; so the family struggled to pull the tree from out of the frozen ground!

It was unbeknownst to Galecki that 25 years later he would be starring in a sitcom that wouldn't include cold weather sets and crazy Christmas decorations, but about a woman that moves into an apartment across the hall from two brilliant yet socially awkward physicists — and that Galecki would be playing one.

This August the three main actors on the show Galecki, Jim Parsons and Kaley Cuoco have earned themselves a hefty salary of $1 million per episode. That's far from what the entire Griswold family likely made back in 1989.

Galecki was also a star on the '90s sitcom Roseanne, which was also filmed live in front of a studio audience. "My experience makes me a bit more schooled in rolling with those changes in front of the audience — it's something I really like, and I think the cast finds it exciting," he told The A.V. Club in an interview. "But as far as the show working as a whole, I had no idea. That's not to say that I didn't have faith in it, but I've done quite a few things that I thought would strike a chord and they didn't. See, you don't know about those because nobody saw them. [Laughs.] But there's no recipe, no matter how hard you work or how hard you commit.