It would be easy to suggest film characters (e.g. Darth Vader), rather than film stars but that doesn't really seem to fit with the theme.
I suggest that it might be best to think of film stars who are known for playing one particular character or one particular type of role. For example, Charlie Chaplin, Stan Laurel, Oliver Hardy and Norman Wisdom all played basically the same character throughout most of their films (so they're easily recognised). John Wayne played many similar roles as well.
I assume from your screen name that you're male but that doesn't prevent you from going to a fancy dress party in drag. A pair of false bosoms and a bikini would quickly turn you into Barbara Windsor (as she was in all those Carry On films). Or, if you think you could carry it off, you might even want to try being Marilyn Monroe for the evening :-)
Chris