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 (2018–2019). 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). Galecki 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, he 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. Early life Galecki was born in Bree, Limburg, Belgium to American parents of Polish, Irish, and Italian descent. His mother, Mary Louise (Mary Lou) Noon, was a mortgage consultant, and his father, Richard Galecki, was a member of the U.S. Air Force stationed in Belgium and worked as a rehabilitation teacher. Galecki is the eldest of three children with a sister, Allison, and a brother, Nick, whom he describes as a "mechanical genius" in the automotive industry. Galecki grew up in Oak Park, Illinois. He dropped out of school after 8th grade, attending high school for only one day. During an interview with New Zealand radio station ZM, Galecki recalled his childhood relationship with his mother. As a child, he was well known for making up long stories and tales. In such situations, his mother used to make him play the "quiet game", where he had to see how long he could go without talking. He also recalled that despite being a loving mother, she was also very tough. One phrase she would lovingly use was, "I love you, now get out." Career After working in the Chicago theatre scene as a young child, Galecki made his onscreen acting debut in the 1987 CBS miniseries Murder Ordained with JoBeth Williams and future Roseanne co-star John Goodman. In 1989, Galecki portrayed Rusty Griswold in National Lampoon's Christmas Vacation. In 1990, he was cast as Danny Nash, the son of Robert Urich's lead character, on the NBC comedy American Dreamer; the following season, he was a regular cast member on the ABC sitcom Billy,