The Change Constant

John Mark "Johnny" Galecki (born April 30, 1975) is a Belgian-born American actor. He is best known for his roles as David Healy in the ABC sitcom Roseanne, Rusty Griswold in National Lampoon's Christmas Vacation, and as Leonard Hofstadter in the CBS sitcom The Big Bang Theory...(Wikipedia)

Credits include: The Big Bang Theory, What the #$*! Do We Know?!, Speechless, Halloween and Movie Poster Contract

Credits include: The Big Bang Theory, Pumpkinhead, Beaches, Don't Drink the Water and Jeopardy!

Credits include: The Big Bang Theory, Why Him?, Virtuosity, The Wedding Ringer and Hop

Credits include: A Serious Man, Evan Almighty, Van Wilder, The Big Bang Theory and Walk Hard: The Dewey Cox Story

James Joseph "Jim" Parsons (born March 24, 1973) is an American television and film actor best known for playing Sheldon Cooper on the CBS sitcom The Big Bang Theory, with his performance often cited as a significant reason for the program's success. On July 16, 2009, he was nominated for an Emmy Award for Outstanding Lead Actor in a Comedy Series for his work on The Big Bang Theory.

Credits include: I Love You, Man, The Big Bang Theory, The Laundromat, Delirious and Are You Here

Credits include: The Big Bang Theory, Trolls, Spaceman, Trolls World Tour and Trolls Band Together

Credits include: Mayor's Day Out, Venus on the Moon, 1-900-Crushed, Henry and the Woodpeckers and The Change Constant

Credits include: The Change Constant