Apart from the voice of Yoda, Frank Oz, have there been any other actors who played a role in both trilogies? I suppose Hayden Christensen counts, having been recently included in the Blu Ray version of Episode VI.
When Lucas was talking about making three trilogies, he said that the droids (R2-D2 and C-3PO) were the only ones that would be in all three trilogies and in all nine movies (this was in the 70s, when he said there would be three trilogies). He said the story was basically told through their eyes.
Excluding The Clone Wars (the movie and both animated series), here's the actors who were in both trilogies (but not always in all films):
Frank Oz, as you have already mentioned, played Yoda's voice in five movies.
Ian McDiarmid played Senator/Chancellor/Emperor Palpatine (and Darth Sidious) in 4 movies (Episodes I-III and VI) originally, but was dubbed in for Episode V later. So you could say he was in four of the movies when they were originally released, but is currently in 5 of the movies.
While some say Greedo showed up in 2 films, one in each trilogy, he was played by different actors in Episode I and Episode IV.
If the Special Editions are taken into account Temuera Morrison is in 3 films, playing Jango Fett and his clones in Episodes II and III and voicing Boba Fett in the Special Edition of Episode V.
What about Chewbacca played by Peter Mayhew, he was in III and IV-VI
You guys forgot Warwick Davis!
He played Wicket in Episode VI (in costume) and also had 4 (uncredited) appearances in Phantom Menace
He had four brief uncredited appearances in The Phantom Menace—one as W. Wald, the young Rodian friend of Anakin Skywalker; the other as Weazel, one of the gamblers at the podrace. Davis also had a cameo as a "Tatooine street trader", and doubled Yoda in some of his "walking" scenes in Episode I
The only characters to appear in both trilogies were Anakin Skywalker / Darth Vader, Obi-Wan Kenobi, The Emperor, R2-D2 and C-3PO, plus the
muppet character Yoda.
The only actor whose face can be seen in both trilogies is Ian McDiarmid (1, 2, 3, 6 added later to 5).
Another actor whose face can be seen is Hayden Christensen who was digitally added later into Ep. 6.
Others that appear on screen but with a body costume, are Peter Mayhew (3, 4, 5, 6), Anthony Daniels (all) and Kenny Baker (all).
And the actors that contributed with their voice are; James Earl Jones (3, 4, 5, 6) and Frank Oz (1, 2, 3, 5, 6).
Now that the cast for sequel trilogy is apparent, we might have some of these actors appear in 3 trilogies on top of obvious 4 appear in their 2nd.
As I remember from seeing "The Empire strikes Back" preview before the initial Australian cinema release in 1980, the Emperor appeared at least in holographic communication with Darth Vader. Vader moved his Star Destroyer to where he could get better reception first. I don't know if that was Ian McDiarmid or another actor.