Ajarn Surachai Sirisute (Thai: สุรชัย ศิริสูตร์, born October 16, 1948), commonly known as Chai Sirisute or Grandmaster Chai, is a martial arts Instructor who is the founder and President of the Thai Boxing Association of the USA and responsible for introducing Muay Thai to the United States. Born in Bangkok Thailand, Sirisute was indoctrinated to Muay Thai at the age of 4, kicking his father's heavy bag for 15 minutes a day.
He formally studied both Muay Thai as well as karate beginning at the age of six. He earned his black belt in Shorin-ryu at the age of 12, an age at which he also started to fight in the ring in Muay Thai. Sirisute fought over 72 fights in Muay Thai and retired as a fighter in 1968, leaving Thailand to teach in America.
Upon arriving in the US, Sirisute managed to befriend and train a notorious motorcycle gang called the Hells Angels, having no idea who they were until the FBI explained it to him. Whereupon, Sirisute volunteered to train the FBI agents.
During the 1970s and early 1980s Sirisute taught at several Southern California colleges: Chaffey College, Claremont Men's College and Cal State San Bernardino and out of his home. His early students included Jim Vanover, Ron Ritoch (former student of Jim Vanover), Bryan Dobler, Mike Goldbach, Reggie Jackson, Glen Hernandez, Don Boyd, and the vice president Chai's Thai Boxing Association, Tony Gneck whom he brought to Thailand in 1982 as the first American team to compete in the Muay Thai World Championships.
In 1978, trained another Martial Arts teacher named Dan Inosanto. Inosanto trained as a student in Chai's backyard and eventually introduced Sirisute to his Jeet Kune Do teaching seminars, which greatly helped Sirisute extend awareness of Muay Thai in the U.S.A. as well as internationally. In 1983 Inosanto introduced Sirisute to Tom Landry of the Dallas Cowboys who soon incorporated Muay Thai into their pre-season conditioning with Sirisute as their instructor until the time of Landry's departure in 1990.
Sirisute currently runs a Muay Thai camp in Oregon each year with more than 200 students from around the world attending. He founded the Thai Boxing Association of the USA in 1968 and has expanded it to more than 16 countries around the world. He maintains a busy seminar schedule travelling around the world teaching Muay Thai today.
Chai Sirisute's notable students include:
- Greg Nelson : MMA Coach
- Dan Inosanto: Filipino-American martial arts instructor best known as a student of Bruce Lee
- Reggie Jackson
- Don Boyd
- Valentine Espiricueta: Founder of the Applied Sport Martial Arts Program, NFL Consultant, Two-Time World Eskrima-Kali-Arnis World Champion
- Pat Tray: Former Navy SEAL (ST6) Trident Martial Arts Woodbridge, VA
- Kevin Seaman: Senior Instructor 
- Balicki, Ron. Gold, Steven (2007). Jeet Kune Do: The Principles of a Complete Fighter, HNL Publishing. ISBN 9-531766-3-0
- Kelly, Perry (2000). Dan Inosanto: The Man, The Teacher, The Artist, Paladin Press. ISBN 1-58160-079-8.
- Sirisute,Surachai.(1987). Muay Thai Kickboxing, Unique Publications. ISBN 978-0-317-54356-8
- Van Schuyver, Mark and Villalobos, Pedro (2002). Fighting Strategies of Muay Thai: Secrets of Thailand's Boxing Camps. Paladin Press. ISBN 978-1-58160-358-3
- Kelly(2000). p.61
- Profile of Ajarn Chai Sirisute
- Ajarn Chai Sirisute and Dan Inosanto in Muay Thai history
- Interview With Dan Inosanto
- Kelly(2000). pp.133-138
- Grahn, Andy (2008), "Greg Nelson: Ultimate Fighter", MMA Writer (inosanto.com)