"What is thy bidding, my master?"
One of the things that THE EMPIRE STRIKES BACK did successfully as a sequel was not to simply repeat the successful formula of its predecessor. STAR WARS gave us a lot of new stuff to be amazed by, from the huge star destroyer flying overhead in the opening, to the droids, the twin suns of Tatooine, the cantina, the force, lightsabers, Chewbacca, Darth Vader, the Death Star, the holographic chess game, etc., etc., which you'd think would be hard for TESB to even equal.
TESB does manage to bring in lots of new stuff from tauntauns and probe droids to the AT-AT walkers, giant space slugs, a first glimpse of Vader's head sans helmet, and cloud city just to name a few. It also introduced a number of long lasting new characters. Among them is our first look at the Emperor.
Mentioned, but not scene, in STAR WARS (Episode IV - A New Hope), the Emperor appears as an imposing giant holographic bust, overwhelming Darth Vader who kneels in submission before him. Vader's status in this movie seems elevated beyond the mere henchman to Grand Moff Tarkin that he was before, but his subservience to the Emperor only adds to the mysterious Emperor's seeming to be all powerful and all seeing.
Heightening this sense of the Emperor being all seeing and all powerful was his strange and eerie appearance. We can't see his face clearly, but there is definitely something that is not normal about it, or inhuman. The Emperor was physically portrayed by an ucredited, and possible elderly, actress who wore make-up appliances to give the upper portion of the face, particularly the eye sockets their peculiar appearance. Enhancing the strangeness were the chimpanzee eyes which were optically superimposed over the eye sockets. The Emperor's somewhat mystical and authoritative voice was provided by Clive Revill, a celebrated stage and voice actor, who has also physically appeared in a number of movies.
This scene was changed following the release of STAR WARS: EPISODE III - REVENGE OF THE SITH. The holographic emperor, chimpanzee eyes, voice and all, were removed and replaced with the Emperor as portrayed by Ian McDiarmid, the actor who played him in STAR WARS: EPISODE VI - RETURN OF THE JEDI as well as the three prequel movies. Additional dialogue was also added to the sequence.
Admittedly, this visual continuity makes a lot of sense, and is one of the least arbitrary seeming changes that George Lucas has imposed on the STAR WARS movies post release, and McDiarmid provides one of the best performances throughout the STAR WARS films, but his incarnation of the Emperor, while evil and creepy looking, does note evoke that same alien mysteriousness that the original did.
In 2008 Hasbro made a really cool toy of this scene for their popular Star Wars action figure line. The toy includes electronic elements which allow the Emperor's hologram to light up and a sound chip which repeats all of the sound and dialogue for this scene.
You can see more image of the toy at Rebelscum where the above image was obtained.