Actor Johnny Galecki's first role was on the Roseanne Barr television movie Backfield in Motion. Barr cast him as David Healy on her sitcom Roseanne. He spent several years on the program and from there played smaller roles in films such as I Know What You Did Last Summer, The Opposite of Sex and Bounce.

Galecki returned to television as Leonard Hofstadter, the leader of a pack of socially awkward prodigies, on the CBS sitcom The Big Bang Theory.

• Note: The majority of the links in this timeline are to IMDb, which has pop-ups.

• April 30, 1975: Born

• 1987: Murder Ordained

• 1989: Christmas Vacation

• 1991: Blossom

• 1992-1997: Roseanne

• 1997: Suicide Kings

• 1997: I Know What You Did Last Summer

• 1998: The Opposite of Sex

• 2001: Vanilla Sky

• 2005: Happy Endings

• 2005-2006: Hope & Faith

• 2006-2007: My Boys

• 2007: The Big Bang Theory