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    "The Big Bang Theory" Is Officially 15 Years Old — Here Are 12 Side-By-Sides Of The Cast Then Vs. Now

    The Big Bang Theory aired its first episode 15 years ago, and the cast has changed quite a lot since then.

    It's officially been 15 years since The Big Bang Theory premiered on CBS. The show went on to have 12 seasons and 280 episodes, and it became one of the biggest comedy series to date. So to celebrate, let's take a look back at the iconic cast members in their first movie or TV roles vs. on the show vs. in real life:

    1. Johnny Galecki's first role in 1987:

    A boyish Johnny's face circled

    Johnny Galecki as Leonard Hofstadter on The Big Bang Theory:

    Johnny in seasons 1 and 2

    Johnny Galecki now:

    2. Jim Parsons's first role in 2002:

    Jim outside and wearing a cap and shirt

    Jim Parsons as Sheldon Cooper on The Big Bang Theory:

    Jim shown in seasons 1 and 12

    Jim Parsons now:

    Jim wearing glasses and a bow tie

    3. Kaley Cuoco's first role in 1992:

    A young Kaley with a short bob and bangs

    Kaley Cuoco as Penny on The Big Bang Theory:

    Kaley in seasons 1 and 12

    Kaley Cuoco now:

    Kaley at the Emmys

    4. Simon Helberg's first role in 1999:

    Simon with spiked hair

    Simon Helberg as Howard Wolowitz on The Big Bang Theory:

    Simon in seasons 1 and 12

    Simon Helberg now:

    Simon with longer hair on the red carpet

    5. Kunal Nayyar's first notable role in 2007:

    Kunal rocking a mustache and being apprehended

    Kunal Nayyar as Raj Koothrappali on The Big Bang Theory:

    Kunal in seasons 1 and 12

    Kunal Nayyar now:

    6. Melissa Rauch's first role in 2006:

    Melissa looking down and then up

    Melissa Rauch as Bernadette Rostenkowski-Wolowitz on The Big Bang Theory:

    Melissa Rauch now:

    7. Mayim Bialik's first major role in 1988:

    Mayim with curly hair

    Mayim Bialik as Amy Farrah Fowler on The Big Bang Theory:

    Mayim in seasons 3 and 12

    Mayim Bialik now:

    Mayim on the red carpet

    8. Kevin Sussman's first notable role in 1996:

    Kevin looking shocked

    Kevin Sussman as Stuart Bloom on The Big Bang Theory:

    Kevin in seasons 2 and 12

    Kevin Sussman now:

    Kevin on the red carpet

    9. Christine Baranski's first notable role in 1982:

    Christine wearing a wide-brimmed hat

    Christine Baranski as Dr. Beverly Hofstadter on The Big Bang Theory:

    Christine Baranski now:

    Christine on the red carpet

    10. Wil Wheaton's first role in 1981:

    Wil as a boy

    Wil Wheaton as himself on The Big Bang Theory:

    Wil in seasons 3 and 12

    Wil Wheaton now:

    Wil in jeans and a casual suit jacket

    11. John Ross Bowie's first notable role in 2000:

    John as a waiter

    John Ross Bowie as Barry Kripke on The Big Bang Theory:

    John in seasons 2 and 12

    John Ross Bowie now:

    12. And finally, Laurie Metcalf's first notable role in 1981:

    Laurie in a street scene

    Laurie Metcalf as Mary Cooper on The Big Bang Theory:

    Laurie in seasons 1 and 11

    Laurie Metcalf now:

    Laurie smiling on the red carpet