John Mark Galecki (born April 30, 1975) is an American actor. On television, he played Leonard Hofstadter on The Big Bang Theory (2007–2019) and David Healy in Roseanne (1992–1997; 2018) and The Conners (2018–2019). Galecki also appeared in the films Prancer (1989), National Lampoon's Christmas Vacation (1989), Suicide Kings (1997), I Know What You Did Last Summer (1997), Bookies (2003), In Time (2011), and Rings (2017). He was one of the highest paid television actors in the world, with his role in The Big Bang Theory earning him approximately US$900,000 per episode between 2017 and 2019. In 2018, Galecki was estimated to be the world's second highest-paid male TV actor by Forbes—behind only his The Big Bang Theory co-star Jim Parsons—earning $25 million. The accolades he has received include a Satellite Award, alongside nominations for a Primetime Emmy Award, Golden Globe Award, and six Screen Actors Guild Awards.