An Acting Instructor is a person, usually well educated in theatrical arts, who teaches, or 'instructs', aspiring performers on various acting methods.
 One example is the French mime artist Jacques Lecoq, whose methodology has inspired several theatre practitioners including Steven Berkoff.
Alexandra "Sasha" Barrese (born April 24, 1981) is an American actress known for her role as Tracy Billings in "The Hangover Trilogy".
Thomas G. Waites (born January 8, 1955) is an American actor and acting instructor born in Philadelphia, Pennsylvania.
 Waites runs an acting studio in New York City which is named for him.
 He has been a member of the Actors Studio since 1984.
Salem Ludwig (July 31, 1915 – April 1, 2007) was an American character actor and highly esteemed acting instructor.
Berg Studios is an instructional, film and television acting studio and theatre space in Atwater Village, California in the Los Angeles area.
 The Studio space is owned and run by acting instructor and Yale Drama School graduate Gregory Berger-Sobeck, who has taught acting in Los Angeles since 1998.
John A. Ellsler (September 21, 1821 – August 22, 1903) was an American actor, theatre manager and acting instructor who helped make Cleveland, Ohio one of the more important theatre towns in post Civil War America.
 Ellsler was instrumental in starting the careers of several well known actors of that period including his daughter's, and had once been a friend and business partner of the assassin, John Wilkes Booth.
Arthur Mendoza was the principal acting instructor for the Stella Adler Conservatory of Acting West.
 He has taught in Los Angeles for more than 20 years and has worked with such talents as Khandi Alexander, Sasha Barrese, Peta Wilson, Finola Hughes, Branford Marsalis, Deidre Hall, John Jopson, and Salma Hayek, and he worked extensively with Benicio del Toro after he won a scholarship to the Conservatory.
 He has performed in more than 124 plays and worked on television and in film, including episodes of Falcon Crest and "Our House" and the film "Deep Cover".
Estelle Harman (September 11, 1922 – April 15, 1995) was an acting coach in Los Angeles.
 She began as an acting instructor at UCLA in the 1950s, then was hired by Universal Studios as Head of Talent to groom their stable of film actors, which included Rock Hudson, Bill Bixby, Tony Curtis and Audie Murphy.
Ed Kovens (1934–2007) was an American SAG, AFTRA, and AEA actor.
 Furthermore he was a Method acting instructor based in New York City.
 He was a member of The Actor's Studio and worked with the legendary Lee Strasberg.
Christine Brubaker is a Canadian actor and director.
 As a theatre actor, she has worked across Canada.
 Well known for her work in the ensemble cast of the A&E TV original series, "A Nero Wolfe Mystery" (2001–2002), she is a regular acting instructor at Sheridan College.
 She currently lives in Toronto, Ontario.

Question: Who was the acting instructor of the actor who played the role of Tracy Billings?
Answer: Arthur Mendoza