Complex sentence: Barber had previously played the character Jimmy Speckerman in an episode of The Big Bang Theory; within the series, Speckerman was a classmate of Leonard Hofstadter who used to bully him.
Split into simpler sentences: Barber had previously played the character Jimmy Speckerman in an episode of The Big Bang Theory. Speckerman is a classmate of Leonard Hofstadter who used to bully him.