Johnny Galecki Leonard Hofstadter Actor Jim Parsons Sheldon Cooper Actor Kaley Cuoco Penny Actor Simon Helberg Howard Wolowitz Actor Kunal Nayyar Raj Koothrappali Actor Melissa Rauch Bernadette Rostenkowski Actor Mayim Bialik Amy Farrah Fowler Actor Kevin Sussman Stuart Bloom Guest Star Michael J. Massimino Mike Massimino Guest Star Pasha D. Lychnikoff Dimitri Guest Star Chuck Lorre Executive Producer, Writer Bill Prady Executive Producer Jim Reynolds Writer Maria Ferrari Writer Steven Molaro Writer Eric Kaplan Writer Steve Holland Writer Mark Cendrowski Director