I'm glad you asked, confused guy from the Getty photo gallery, because it's easier to explain by example. I'm talking about relatively unknown actors who made two completely distinct lasting impressions. You probably don't know his or her name, and you probably didn't even realize it was the same actor in both roles, yet the performances stayed with you as two distinct, iconic roles, while the actor who played them has remained obscure. Well, if you're good enough to occupy the public's imagination in two performances so dissimilar that most people don't even realize the parts are played by the same person, you deserve a shout-out, even if no one knows your name.
NOTE TO READER: Are you with me? This is not an article about actors who've played lots of different roles, or even actors like Gary Oldman or Daniel Day-Lewis, who've been almost unrecognizable in various roles. This is a salute to obscure actors who seem to have caught lightning in a bottle twice, with two popular roles that they disappeared into so completely, most people don't even realize they were played by the same actor. Still not with me? Try setting yourself on fire and see if that helps. Or just start reading.