In Jose Rivera's two-man play entitled, "Tape," the Attendant (the supporting character) is a foil for the Person (the protagonist).
A foil is used in fiction; it is a character whose presence provides a comparison with the main character, thereby providing a clearer picture of the protagonist.
[A foil] highlight[s] various features of that other character's personality, throwing these characteristics into sharper focus.
At the same time, development of the Attendant (the supporting character) takes place.
Though it may not seem clear at first, this short production is a form of tragedy, at least as far as the Greeks and/or Aristotle would see it. The Person finds himself either in Heaven, hell, and/or at Judgement Day. He is being required to relive his sins by listening to the lies he has told throughout his life, and there are many of them.
The Attendant tries to accomodate the Person with answers to questions he is asking as the Person tries to understand what lies ahead of him. The Attendant tries to be supportive and kind, while the frustrated Person becomes almost verbally abusive. The Attendant is patient but sad, perhaps because he has seen this kind of situation transpire before. The kinder and more attentive the Attendant is, the more distressed the Person becomes. Throughout the exchange between the two, the development of the supporting character (the Attendant) sheds a clearer light on the Person, and we are perhaps less surprised that there are ten thousand boxes of tapes outside of the room, filled with his lies, that he must listen to, for as long as it takes. Rather than face life head-on, he has perhaps taken the easier path of lying. This is what we see at the play's end when the Person is face with what seems to be his mother, asking where he has been, and the Person prepares to listen to his first lie.
The presence of the Attendance provides a much clearer picture of the Person in the play.