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Born in 1975, Johnny Galecki is an American actor best known for his role as Leonard Hofstadter in the popular sitcom "The Big Bang Theory." He began his acting career in the late 1980s, appearing in television shows and films such as "Roseanne" and "National Lampoon's Christmas Vacation." Galecki has also starred in the films "In Time" (2011) and "The Ring" (2002).