In my mind, there’s one that always comes to mind. It’s Anthony Daniels. He carries a lot of the first film and provides pitch perfect comic relief in the second, in a role that could have very easily been a disaster. And he really was a big part in establishing the 3PO personality we know, as Lucas had other plans in mind (used car salesman). Same goes for Frank Oz of course (lesser extent due to not appearing in the first film).

Cushing deserves a lot of credit for knowing exactly what film he was in and nailing it, but if you’re going the ‘veteran actor lends credibility’ route, the answer is obviously Guinness. The film doesn’t work without the gravitas he provides to Luke’s story. I think you could switch out Tarkin with a lesser actor but you can’t switch out Guiness with a lesser actor.

Ford’s skills are obvious, and of course Star Wars is nothing without the cool factor he brings. But credit due to Hamill and Fisher as well, they aren’t the best actors ever of course but they fit so well into those roles. Every time I see the audition tapes of actors they didn’t go with I’m reminded of that.