[1] He began his formal martial arts training at age 10, studying tang soo do under a cousin who operated a dojo owned by Chuck Norris.

His willingness to compete internationally led him to fight and train in Japan, where he embraced his Japanese heritage en route to becoming one of the country's most popular sports stars.

[2] In May 1989, Nielsen entered world-class competition by challenging budding superstar Kevin Rosier for his WKA World Super Heavyweight Championship.

The fight ended in the sixth round when a visibly angered Rosier threw Nielsen onto the ring ropes and landed an unprotected blow to the face, leading to a technical knockout.

[5] Nielsen attempted to make up for this loss later in the year with a contest against Rob Kaman, a Dutch Muay Thai stylist attaining legendary status as an international champion.

Nielsen sought to match his opponent's signature low kicks but found himself repeatedly swept by Kaman's legs before being knocked out by a surprise right hook.

On October 4, 1992, he met Ken Shamrock in a mixed rules bout - the first time in Japan that a pro wrestler had fought a kickboxer in televised no-holds-barred competition.

Beginning in 1987, he traveled to Thailand to train at Muay Thai gyms, where he treated his fellow kickboxers and learned that chiropractic wasn't widely practiced in the country.

He subsequently partnered with Paolo Memorial Hospital and participated in monthly charity tours – offering chiropractic treatment to far-flung and impoverished villages.

[4] As chiropractic was not yet adopted by Thailand's Ministry of Public Health, Nielsen's enterprise brought him into conflict with authorities - at one point being arrested and charged with practicing medicine without a license and running a clinic without a permit.

An aggressive fighter characterized by his powerful striking ability, Nielsen synthesized his boxing and martial arts skills into a formidable offensive technique.

Future K-1 Grand Prix '94 runner-up Masaaki Satake was able to control his rematch against Nielsen with counter strikes, and multi-time world champion Rob Kaman knocked him down repeatedly during their bout with his signature low kicks.