Demetrious “Mighty Mouse” Johnson has earned his nickname.

The five-foot-three, 125-pound UFC flyweight champion successfully defended his title in June for the fourth time in his career. In December of last year, the 27-year-old knocked out his opponent during the first round, earning a $50,000 bonus and “Knockout of the Night” award.

A Puyallup resident, Johnson trains out of the AMC Martial Arts gym in Kirkland. Johnson first acquired the “Mighty Mouse” name due to his smaller stature compared to the other fighters he sparred with at the gym. But as his record shows, his fighting abilities are nothing to joke about, with a total of 20 wins out of 23 professional fights, four of those won by knockout.

A wrestler at Washington High School in Parkland, Johnson won third and second place at the state championship meet the Mat Classic. Although he said he doesn’t employ wrestling in his strategy, he said the training regimen of cutting weight to remain in the right weight class, fighting in a confined area and taking instructions from coaches, laid the groundwork for when he began fighting professionally.

“It’s almost identical,” he said of the training habits for the two sports.

Johnson said he got into fighting after high school because he was attracted to the individuality of the sport and its viability as a career compared to the Olympics.

“How much work you put in is how much you get out,” he said. “Nothing dictates what’s going to happen. It’s all my work and I love working hard. Even in wrestling that’s what drew me in. You have a team, but it’s all you [on the mat] and that’s what gravitated me towards fighting. You can go to college and the Olympics, but there’s no money and you have the rest of your life to figure out what you’re going to do.”

Johnson entered his first professional fight in 2007, which he won in the first round by a knockout. By that time he had already participated in more than two dozen amateur fights.

“I was pretty seasoned by then when I made that next leap,” he said. “I was ready to go.”

In many of his fights, Johnson demonstrated his ability to pull off a victory as an underdog. In a 2011 fight against Miguel Torres, Johnson managed to win despite breaking his fibula during the second round, which Johnson said was the result of an old wrestling injury.

His record is also remarkable considering many of his fights were against bantamweight fighters, who weigh between 135-145 pounds. It wasn’t until 2012, when the first UFC flyweight tournament ever was held, that Johnson was able to compete against fighters his own size. Johnson ultimately won the tournament, earning the UFC flyweight champion title.

Currently, Johnson trains five days a week out of the Kirkland gym, run by his trainer and fellow fighter Matt “The Wizard” Hume.

“My coaches are huge,” he said. “They’re always helping me, forcing me to learn new things, to make the right decisions when it comes to training.”

Despite his insistence on hard work while training, Johnson said one of the most important things for a successful fighter is to not overtrain, which he said leads to unnecessary injuries.

“You want to train just enough but not injure yourself,” he said. “That’s how you prolong your career.”

As for his own career, Johnson said he has no definite plans beyond the next fight.

“I’m going to take it one step at a time,” he said. “I don’t know if I’ll ever walk away from the sport. Hopefully I can put in 10 more years and keep on making money.”