Who is Shepherd of Laius from Oedipus the King and what is their importance?

The Shepherd of Laius is summoned by Oedipus so he can confirm his true parentage. The shepherd doesn't want to reveal the truth and only does so after his life is threatened.The shepherd admits to receiving an infant, as well as giving the infant to Polybos's messenger. After hearing the shepherd's tale, Oedipus becomes aware of his real identity, even worse, he now knows that he is not only responsible for his father's death..... he is married to his mother.