Johnny Galecki as David Healy Johnny Galecki might have got his start as Darlene's boyfriend (and later, husband) David, but the 42-year-old has since carved out a name for himself as Leonard Hofstadter on The Big Bang Theory. He's been in 245 episodes of the CBS sitcom, as well as movies like Rings and CBGB. Image Sources: Everett Collection and Getty / Michael Loccisano