From Muppet Wiki

The Spook appeared in The Wizard of Id pilot. In the original comic strip, the Spook is a longtime prisoner in The King of Id's dungeons, and his entire body is coated in hair, with only a nose and limbs peeking out. The Muppet version of the character was green, appearing to be refurbished from an earlier monster character. The Spook has only one line, "Let me out!", but takes an extended bow in the closing scene.