Mike Tyson was so vicious and overdeveloped as a 12-year-old that he mixed it up with grown blokes, according to his former coach.
'Iron Mike' had to do battle with a 27-year-old professional boxer when he first set foot in the gym but weighing over 13 stone and with no fat on his body, he wasn't fazed by the step up and would regularly knock out adults inside the squared circle thanks to his unparalleled power.
"He had to impress me and Cus [D'Amato, Tyson's legendary trainer]," Teddy Atlas told RingTV.
"He had to box his first day with a 27-year-old man who was a professional fighter, and he was able to do that.
"You can't put him in with kids to spar because there are none. So you're hiring sparring partners and they're men and he's hurting them and knocking them out.
"Anyone who could be knocking out men when he's 12, 13 years old is a pretty damn good puncher. He learned the technique to make you miss and catch you clean but power's power and punchers are born not made."
Tyson, who won 50 of his 56 fights, producing 44 knockouts in his career, is still referred to as the 'Baddest Man on the Planet' to this day.
He feared absolutely nobody in the ring and even had the nerve to live with a pet tiger. But Tyson was very much scared of Cus D'Amato, his first trainer and the man credited with helping Tyson unlock his ferocious power.
Writing in his book 'Iron Ambition: My Life with Cus D'Amato' released in 2017, Tyson explained: "I was petrified when I was alone with him.
"If he called me - 'Mike, I need to talk to you' - I didn't feel good going over to him.
"That's when he'd start giving me his detailed criticisms of my fights."
The 53-year-old also said the public didn't see behind the curtain and past the in-ring celebrations.
"People see the public celebrations of my sensational knockouts but they don't hear Cus talking to me alone after the fight!
"He'd make me feel like s***, play with my emotions. He would put things in your head all day."
Tyson became the youngest world heavyweight champion aged just 20 back in 1985 and dedicated his victory to Cus, who had died one year previously.