RALF was the nickame for an early version of the ALF puppet that was used during rehearsals to avoid wear and tear on the principal ALF puppet.
According to the creator and voice of ALF, Paul Fusco, the RALF puppet is still in existence.
Paul Fusco stated in an interview that RALF is an acronym for Rehearsal Alien Life Form. It is known that RALF had only one on-screen appearance where he appeared in a car. This screen-cap was from Season 3 ep. "Alone again, Naturally". Alf thinks he saw his cousin Blinky.