By Emily Krauser
6:13 PM PDT, May 3, 2019
Bazinga! After 12 seasons on air, The Big Bang Theory is coming to an end after clocking in a whopping 279 episodes. Before we say goodbye to the beloved sitcom with its series finale on May 16, let's take a look back at how much Sheldon, Leonard, Penny and company have changed from season one to today.
Jim Parsons: Then

Sheldon Cooper, season one.
Jim Parsons: Now

Sheldon Cooper, season 12.
Johnny Galecki: Then

Leonard Hofstadter, season one.
Johnny Galecki: Now

Leonard Hofstadter, season 12.
Kaley Cuoco: Then

Penny, season one. (Fun fact: she's the only main character who's last name has never been revealed.)
Kaley Cuoco: Now

Penny, season 12.
Simon Helberg: Then

Howard Wolowitz, season one.
Simon Helberg: Now

Howard Wolowitz, season 12.
Kunal Nayyar: Then

Rajesh Koothrappali, season one.
Kunal Nayyar: Now

Rajesh Koothrappali, season 12.
Mayim Bialik: Then

Amy Farrah Fowler, season four (Bialik's character was first introduced in the season three finale.
Mayim Bialik: Now

Amy Farrah Fowler, season 12.
Melissa Rauch: Then

Bernadette Rostenkowski, season three.
Melissa Rauch: Now

Bernadette Rostenkowski, season 12.