There is this actor or actress and s/he's famous for this role in XYZ.
Except you never watched that. Or you only watched it years after you've come across the actor.
To me that fits on (at least) two actors who both originated in the horror genre (a genre that does not interest me at all).
The first one is Bruce Campbell. To pretty much all of his fans, he is the guy from the
Evil Dead series. To me, he was first and foremost Brisco County, jr. and my recognition of him cemented when he became the master thief Autolycus on
Hercules and
Xena.
The second one played the decent Visitor
Wilie on
V. I vividly remember him running back into an accident site to rescue a Human co-worker from being turned into a liquid nitrogen popsicle. To everyone else, he's
Freddy.