#12 Ken Shamrock (1993 to 2016)
Ken Shamrock competed at UFC 1 in November 1993 and was many observers pick to win the inaugural tournament given his impressive physique and credentials. It was considered a major shock then when he cleanly submitted to the much smaller, Royce Gracie in the semi-final.
However, Shamrock would be back. He competed in Pancrase simultaneously with UFC and after withdrawing from the UFC 3 tournament final due to injury, he got his opportunity at a re-match with Gracie at UFC 5 and dominated him for 36 minutes. The lack of judges during the early years of the UFC were the only thing that prevented him from victory. Shamrock instead had to settle for a draw.
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At the following UFC, he defeated Kimo to become the company's first Superfight Champion; a title he held until UFC 9, when he dropped it to Dan Severn on a Split Decision.
Shamrock fought just once more in MMA before joining the World Wrestling Federation after MMA and UFC in particular was forced underground by the United States government.
Due to the worldwide fame he achieved in the WWF, PRIDE in Japan, made Shamrock a massive financial offer to return to MMA in 2000. He did so and the 36-year-old returned with a bang by becoming the first man to ever stop Alexander Otsuka in a fight.
Two years later, he contested the fight of the year with Don Frye at PRIDE 19 when despite wrenching Frye in an Ankle Lock for over five minutes, found himself on the wrong side of a Split Decision.
Shamrock's performances earned attention from his old friends at UFC and he was offered a return bout versus Tito Ortiz, with whom he had had bad blood for years.
UFC 40, built by the hype of Shamrock's return earned the promotion it's biggest buy-rate in well over half a decade, pulling 100,000 orders. Shamrock had brought UFC back into the mainstream, where it has stayed ever since.
Shamrock's next UFC bout saw his final victory inside the Octagon wherein he defeated Kimo once again in a heavily hyped re-match.
From there, Shamrock had mixed fortunes in MMA. He dropped two more matches to Ortiz in UFC, before he won just two of his final seven fights. Although his losses to Mike Bourke and Gracie were shrouded in controversy.
Shamrock did fight long past his prime; that much is true, but in terms of influence on the sport and the fighters he trained in the Lion's Den, well rounded fighting ability, drawing power and importance to the entire sport, few can match the "World's Most Dangerous Man."