One of things that makes The Big Bang Theory such a fun show is its occasional special guest appearance.
There have been several memorable cameos throughout the show's eight seasons, including famous scientists and beloved actors.
Some have appeared to play other characters, but the moments we love most are the ones where the gang completely geeks out over an actor or has an inappropriate response to a renowned scientist.
So, here they are: our list of 17 special guests who appeared as themselves and had some... interesting interactions with Sheldon, Leonard, and the rest of the group.
Yes, many of these come from Star Trek, but you're not surprised about that, are you? Rest in peace, Leonard Nimoy.
If you've missed any of these wonderful appearances, you can watch The Big Bang Theory online to see who you can catch.
Up next is The Big Bang Theory Season Season 8 Episode 17, "The Colonization Application." Be here shortly afterward for a full review of all the fun!