To obtain a 10th Dan Shotokan Karate Black Belt, it usually takes a minimum of 5 years of continous training for a 9th Dan.
The Shotokan 10th Dan grade is the 20th and highest possible level of a practitioner of this Martial Art. Achieving this grade is exceptional, meeting someone at this level should be cherished.
Full guide on this Martial Arts style here: Shotokan Karate
For a guide to other ranks: Shotokan Karate belts
An 10th Dan Shotokan Black Belt in action
Pictured is Hidetaka Nishiyama (October 10, 1928 ~ November 7, 2008) was a Japanese-American martial arts master, instructor, author, administrator and pioneer. A student of Gichin Funakoshi, the founder of Shōtōkan-ryū, Nishiyama is considered one of the great masters of the shotokan karate.
On November 1, 2003, Nishiyama was awarded his Judan, or tenth degree black belt, the highest rank available in Shotokan karate.
Nishiyama sensei died on November 7th, 2008 in Los Angeles.