Hwa Rang Do is purportedly a Korean martial art. However, its origin is Daito-Ryu Aiki-Jujutsu.
"Blackbelt" magazine has run a three-part interview with the "founder" of Hwa Rang Do and, in it, he admits that the techniques are drawn from his training in Daito-Ryu Aiki-Jujutsu and Kodokan Judo (which has been documented) and Korean techniques from a "monk in the mountains" (completely undocumented and unsubstantiated). Such is the case with Hapkido as well.
Technique-wise, it is a combination of Aiki-Jujutsu and Judo throwing techniques with some Tae Kwon Do styles kicks and punches.
Some practitioners of this system often make the claim that this was the fighting system practiced by Hwa Rang warriors of medieval Korea (models for the Japanese Samurai). This is an utter nonsense. No one alive knows what the Hwa Rang practiced, because there has been nothing left of them for hundreds of years. In all probability, Hwa Rang mainly trained in horsemanship, spear fighting, sword fighting and archery. What little unarmed training they had was probably based on Chinese systems (based on documentary evidence).
Hope that helps.
Skorzeny
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For to win one hundred victories in one hundred battles is not the acme of skill. To subdue the enemy without fighting is the supreme excellence. Sun Tzu