The demon's appearance and voice were achieved through a combination of:
* Makeup and Special Effects: The makeup and prosthetics for Pazuzu were created by Dick Smith.
* Puppetry: A life-sized puppet was used for some scenes, particularly when Pazuzu was depicted as a full-bodied demon.
* Voice Acting: The demonic voice was provided by Mercedes McCambridge, who won an Academy Award for Best Supporting Actress for her chilling performance.
So, while there isn't one person who "played" Pazuzu, Mercedes McCambridge is the voice you most strongly associate with the demon.