Of course you know that Michael Dorn's Klingon character Worf would appear in both "Star Trek: The Next Generation" and later "Star Trek: Deep Space Nine."
But did you know that Worf almost ended up on "Star Trek: Voyager"? That's right, the original plans were to include Worf on Capt. Janeway's crew, which would've made it pretty hard for the character to come back for cameos in the later films featuring the TNG crew.
Luckily, Dorn nixed the idea, but changed his mind when offered a prominent role in "Deep Space Nine."

Perhaps today is a good day to turn down a series ...