With The Big Bang Theory running as long as it did, it's no surprise that it spawned its fair share of hilarious running gags ...

Johnny Galecki is probably the best-known Roseanne veteran to have appeared on The Big Bang Theory, but he's far from the only actor to pop up on both shows.

The biggest speculation in The Big Bang Theory and Young Sheldon fandom is that Leonard Hofstadter, Sheldon's best friend, is potentially dead.

Young Sheldon's finale floated the idea that Leonard may be dead, but now The Big Bang Theory franchise is one step closer to solving the mystery.