National Lampoon's Christmas Vacation
John Mark Galecki (born April 30, 1975) is an American actor. He played Leonard Hofstadter in the CBS sitcom "The Big Bang Theory" (2007–2019) for which he received a Primetime Emmy Award nomination, and David Healy in the ABC sitcoms "Roseanne" (1992–1997; 2018) and "The Conners" (2018–present). 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).