For absolutely no good reason, this struck me the other day.
Before they were caricatured in the first Mad magazine Star Wars parody (Star Roars), most of the leads had already been caricatured in other movie parodies.
Alec Guiness probably appeared in other parodies, but he was certainly in Flawrence of Arabia back in 1964 (drawn by Mort Drucker).
Harrison Ford was in the parody of American Grafitti (also by Drucker)
Carrie Fisher was in the parody Shampooped (by Angelo Torres, I think)
Even David Prowse appeared in A Crockwork Lemon back in 1973.
That leaves Mark Hamill as the only main on-screen actor not previously caricatured.
(I don’t count Peter Mayhew, Anthony Daniels, or Kenny Baker, for obvious reasons. James Earl Jones doesn’t appear onscreen, although I suspect he’d been caricatured earlier. The only other “name” actor was Peter Cushing, who may well have been done before, but I can’t recall it. )