Johnny Galecki plays nerd physicist Dr. Leonard Hofstadter on the CBS situation comedy The Big Bang Theory. Johnny Galecki was born in Belgium but grew up outside of Chicago, where he began his career in community theater when he was just 7 years old. He landed the role of Rusty Griswold in the 1989 comedy film Christmas Vacation, and he's been working as an actor ever since. Galecki relocated to Los Angeles when he was only 14, to take a job on the sitcom American Dreamer (1990). After several small roles in television, he joined the hit series Roseanne during its fourth season (1992). Until the show ended in 1997, Galecki played David Healy, the mop-topped boyfriend of Roseanne's daughter, Darlene (played by Sara Gilbert). He spent the next several years working on stage and in films, but Galecki didn't break out of the "out that guy" club until the success of The Big Bang Theory. The show began in 2007 and slowly built a loyal audience; by 2009 it was an Emmy contender in several categories. Johnny Galecki's feature films include Suicide Kings (1997, with Christopher Walken), The Opposite of Sex (1998, with Lisa Kudrow) and Vanilla Sky (2001, starring Tom Cruise and Penelope Cruz).
Johnny Galecki and The Big Bang Theory co-star Kaley Cuoco announced in 2010 that they had secretly dated each other for two years.