Johnny Galecki

John Mark "Johnny" Galecki (b. 1975) is an American Emmy-nominated actor. He is best known for playing the role of Rusty Griswold in National Lampoon's Christmas Vacation.

Galecki will appear on Sesame Street to explain the word "transform" in a Season 42 Word of the Day segment.

His television credits include Roseanne (as David Healy, first introduced as "Kevin") and The Big Bang Theory (as Leonard Hofstadter).