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About OC Martial Arts

Sensei David and Master Kevin Griswold in 90’s
Sensei David and Master Steven Kim 2024

A rich martial arts journey spanning 40 years. Sensei David started his martial arts journey at the age of 4 training in Karate under Sensei Bob Pavelski. In Middle School he trained in Aikido, Jodo and Iaido under Master Robert and Elise Simmons. He also played tackle football in Middle School, and was a first string varsity OL as a freshman in High School. While playing football he took private lessons in Muay Thai, Jeet Kune Do and Karate under Scott Hennely until he met his fate against Hapkido.

When sparring with a friend in High School at lunch, he threw a roundhouse kick at his friend and found himself flat on his back wondering what happened. What happened was basic hapkido kick defense throw. Sensei David was sold on Hapkido from that point forward. He quit Football and signed up at the California Hapkido Academy in Corona CA under Master Kevin Griswold.

Sensei David trained under Master Griswold until 1999 earning his red belt in Hapkido. Cross training in Brazilian Jiu Jitsu with students of Pedro Carvalho, Jon Munoz, and Joe Moreira.

Master Griswold’s lineage starts with Jang Mu Won Hapkido under Great Grandmaster Chong Song Kim, then Kwang Sik Myung and finally Great Grandmaster Ho Jin Song of Songs Hapkido in LA.

Sensei David trained a group of fellow High School students in submission grappling, and challenged a local CIF State wrestling team to a submission match-emerging victorious. With his passion for martial arts and successful teaching, he went on to teach martial arts at local parks and community programs.

Granmaster Jackie Cotton

In the early 2000s, Sensei David continued his martial arts training under Grandmaster Jackie Cotton in Shaolin Goju-Ryu, through the Shinjimasu Martial Arts Association in Pasadena, California. In 2002, he earned his 1st Dan Black Belt after winning the 3rd Generation Martial Arts Championship in Texas and being victorious in WKO Extreme Fighting in Burbank.

With more success Sensei David trained fighters in MMA at the Westminster High School wresting gym. And taught Kickboxing at Chaffey Community College. Sensei David’s fighters competed in LA at Antonio McKee’s fight promotions. He also assisted in training fighters in LFA, King of the Cage, and K1 Kickboxing.

Sensei David and Brian Warren

In 2009 after having kids, Sensei David shifted his focus to private lessons and training with friends in order to devote time earning a Bachelor of Science in IT and balancing time with his kids. After earning his degree and having a successful career in Software Development, he felt called to return fully to his martial arts path—this time with renewed purpose..

Determined to continue his advancement in Hapkido, Sensei David searched throughout Southern California for the right instructor. In 2024 he started training under Master Steven Kim of OC Mudo in Laguna who is also VP of Sugi Hapkido Federation. Master Kim is a Master of multiple styles including Hapkido, Judo and Jiu Jitsu. Master Kim has trained under Grandmaster Bong Soo Han, Kwang Sik Myung and Yon Gul Son in Hapkido.

In October 2024, Sensei David earned his 1st Dan Black Belt in Hapkido under the Sugi Hapkido Federation, tested by Master Steven Kim and Grandmaster Yon Gul Son. Now holding a black belt in both Hapkido and Karate.

The path to earn a Black Belt in Hapkido was a long and demanding—but deeply earned. Sensei David continues to train under Master Kim. Actively pursuing his 2nd Degree Black Belt, while cross-training with other schools and disciplines to deepen his understanding. He believes being a student of martial arts never ends, and each lesson is best learned with a white belt mentality.

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Master Kim, Master Pak and David
Sensei David and Grandmaster Turner
Sensei David and Grandmaster Son

Testimonials

See what students say about training with Sensei David

“The Greek, the master martial artist we’ve looked up to for decades. Thank you for being an example and for generously sharing your extensive knowledge “
Gabe P.

Martial Artist

“I learned a lot from you back then in the wrestling room after hours putting in work. I was green and you helped me with a lot. Respect to you always and I never forget it!” 
Vincent A.

MMA Fighter

“Not everyone can teach…I know, I have been around Martial Arts for twenty Years. David Can teach! I am a better Martial Artist because of David…Thank you” 
Dennis D.

Shodan, Budoshin Ju-Jitsu Yudanshakai -American Ju-Jitsu Association

“This class made me stronger and gave me more endurance. Something I will need when I go into the ARMY. The class made me a skilled fighter that one day could save my life or the life of others. I thank David for all the skills he has passed on to me and all the lessons in life he has taught me. I am now a greater person then I ever was.” 
Jeff S.

Student

“David was not only an excellent coach for my fight debut, which I won in the first round, but his integrity and trust earned my friendship for the long haul. He was an incredible coach and teacher in my climb through the complicated field of MMA. He brought a sense of realism and understanding to every class. His strengths and proficiencies brought me from a basic level of understanding to amateur fighting status in a short year.” 
Aaron G.

CEO/Personal Trainer/Marine

“I’ve had the pleasure of training and enhancing my martial arts abilities with David while under the Shinjimasu Martial Arts Association. David is a high skilled and disciplined martial arts practioner. I recommend all parties interested in learning the mental and physical aspects of martial arts to experience the training of Mr. Demetroulis.” 
Jamal J.

Actor/Martial Artist

“I’m instructor rank now in Capoeira after 13 years, and Sensei David helped me get started, and get my Quebrado name! I always appreciated your martial arts demos!” 
Randy C.

Capoeira Instructor/Musician