Anthony "Rumble" Johnson, one of the most feared fighters in mixed martial arts history, has died at the age of 38. "Horrible news: Anthony 'Rumble' Johnson passed away today," MMA journalist Ariel Helwani tweeted Sunday. "He was 38 years old. Johnson had been battling an illness for quite some time. One of the hardest hitters and most talented fighters in MMA history. Gone way too soon. May he rest in peace." Johnson, who fought in the UFC twice and was ranked as the No. 2 light heavyweight in the world at the time of his death, was known for his one-punch knockout power and had 17 of his 23 professional victories via KO/TKO, ESPN reports. Tributes to Johnson were pouring in from around the MMA world, with former UFC champion Daniel Cormier tweeting: "Rest Easy my brother. For a guy who struck fear in so many peoples heart Anthony Johnson was a caring person. From random text to check ins during loss. What a person he was, Rumble will be missed. Sometimes life doesn't seem fair."