Johnny Galecki, American actor

John Mark Galecki is an American actor. In television, he played Leonard Hofstadter on The Big Bang Theory (2007–2019) and David Healy in Roseanne 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).