Before mixed martial arts broke into the mainstream, led by Ronda Rousey and Conor McGregor, it still had a core of fanatical followers. And among those early adopters there was no more revered figure than the heavyweight Fedor Emelianenko. Yet he never fought in the Ultimate Fighting Championship.

Emelianenko, a Ukrainian-born Russian, became a cult favorite of early M.M.A. fans for a string of devastating knockouts and an eight-year, 28-match undefeated streak that came in promotions like Rings, Pride and Strikeforce. Many of his bouts were in Japan, where M.M.A. was booming. That meant that for American fans, the fights were often not seen on television but glimpsed in clips dug up online, which somehow deepened Emelianenko’s legend.

His winning streak is long over. But Emelianenko is still fighting at age 42 and will go on Saturday in a Bellator heavyweight semifinal against Chael Sonnen, 41, a U.F.C. veteran, at the Nassau Coliseum in Uniondale, N.Y.