Who is The Invisible Guests from Four Plays and what is their importance?

The true nature of the invisible guests is an important dramatic question about The Chairs. On the one level, they can easily be seen as manifestations of the Old Man and Old Woman's delusions. Since the Old Man and Old Woman are, to some degree, archetypal representations of an essential aspect of humanity (the need to have existence recognized), the invisible guests can themselves be seen as archetypal representations of what the author and his core philosophy (absurdism) suggest is the reality - that individual existence has no recognizable value or meaning. In other words, because the Old Woman and particularly the Old Man believe the guests have come to acknowledge the Old Man, their invisibility suggests that the Old Man's desire for acknowledgment, for having his very existence valued, is a delusion.