the guy who plays leonard on big bang theory
Johnny Galecki John Mark Galecki (born April 30, 1975)[1] is an American actor. He is known for playing Leonard Hofstadter in the CBS sitcom The Big Bang Theory (2007–present) and David Healy in the ABC sitcom Roseanne (1992–1997; 2018). Galecki also appeared in the films National Lampoon's Christmas Vacation (1989), Prancer (1989), Suicide Kings (1997), I Know What You Did Last Summer (1997), Bookies (2003), In Time (2011), and Rings (2017).