In what are called the “modern” Budo, such as Kendo, Aikido, Judo, Karatedo, and so on, ranks are based on the dan-kyu system. As far as most researchers can tell, the system was devised (or if not totally devised, then adapted and wildly popularized) by Kano Jigoro, the founder of Kodokan Judo.
~ Wayne Muromoto from, http://classicbudoka.wordpress.com/2009/10/22/dan-and-kyu-and-youre-welcome/
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