Gennady Golovkin's Jekyll and Hyde persona has helped him become boxing's biggest global star, according to the people who guide his career.
A global audience of millions in over 100 countries will tune in live to watch boxing's most entertaining fighter defend two (WBC and IBF) of his three world middleweight titles against Britain's Kell Brook at the O2 Arena in London on Saturday.
It is not just in his native Kazakhstan that Golovkin (35-0, 32 KOs) -- known as GGG -- is adored. He has a growing army of fans across his adopted homeland in America and millions watch his bouts in Mexico, where fight fans consider him one of their own.
The 34-year-old's promoter Tom Loeffler has seen Golovkin's fame grow since his company K2 Promotions took control of the boxer's career in 2010.
"His popularity with each fight is growing dramatically and this fight will be shown live in over 100 countries," Loeffler told ESPN.
"When he sold out Madison Square Garden against David Lemieux it was a huge accomplishment for him and he was the first non-American to do that.
"But it's not only New York. He sold out the Forum in Los Angeles, that was a big statement on where his popularity is at in the US. Usually in America boxers are only popular in one region, so that's a testament to his phenomenal popularity.
"I think it was over a million viewers for Gennady's fight against Martin Murray on Channel 5 and he's always been very popular in Mexico where 6.1 million saw his fight against Murray.
"One thing that's important to remember about Gennady is his international popularity. He has a universal appeal.
"This fight is the first time he has done a deal with RTL in Germany, one of the biggest networks there. So on an international level his popularity has been increasing. He's very popular Japan for instance, they have shown every one of his fights. He's a fans' favourite in Latin America too.
"American fighters don't leave the U.S. to fight but it's always been part of our plan to keep his international popularity and that's why he has fought in Monte Carlo three times, the Ukraine and Panama and now London."
Loeffler believes Golovkin's burgeoning popularity is not just because of his dazzling displays in the ring.
Golovkin is winning over a U.S. audience despite limited -- but improving -- English and it seems every fight now is building up towards an epic encounter with Mexcian Saul 'Canelo' Alvarez next year, unless Brook (36-0, 25 KOs) can upset the odds.
"A big part of it, even if he doesn't speak perfect English is his personality and respect for opponents and the sport is why people generally like to cheer for him," Loeffler added.
"A lot of great boxers aren't that likeable but like to cheer for Gennady and support him.
"He's exciting inside the ring and he's likeable outside the ring as well. It's the Mike Tyson effect, fans just want to see him.
"His English is getting better and that certainly helps. He has lived in L.A. for the last year and half and he has trained in Big Bear (California) for the last six years. He is becoming more well known in America with each fight."
Golovkin, who lives with his wife and eight-year-old son in California, avoids trash talking but fans still tune in as he brings knockouts.
The WBC-IBF-WBA world middleweight champion has stopped his last 22 opponents and is a big betting favourite to beat Brook, who is stepping up two weight divisions.
Golovkin operates with the clinical precision of a surgeon in the ring but away from the sport, appears to be polite, cheerful and almost innocent.
Martin Murray, who lasted 11 rounds -- longer than any other opponent -- with Golovkin, socialised with the champion following their fight in February, 2015.
"He doesn't speak much English but he's a good guy and a nice person," Murray said.
"He goes out and wreaks havoc in the ring and comes out and he's nice as pie. That's why I'm really happy for all the credit he gets because he deserves it."
Max Hermann, along with his brother Oleg, has been working as Golovkin's manager and advisor since 2009 and says the boxer has been unaffected by fame.
"He's a very calm person and a normal guy outside the ring, down to earth and very polite," Hermann said.
"He hasn't been affected by his success at all. Away from boxing, he's a big football fan and likes playing football and tries to spend time with family when he is not training for a fight. He has seen Manchester United play and likes AC Milan and Real Madrid as well."
Golovkin will be the biggest overseas boxing star to fight in the UK since Kostya Tszyu fought Ricky Hatton in 2005 or Mike Tyson's appearances in 2000.
A crowd of 80,000 saw British super-middleweights Carl Froch and George Groves slug it out at Wembley Stadium in 2014, but Golovkin-Brook has more international interest and significance.
Broadcasters from the U.S., Latin America, Germany and the UK will be ringside on Saturday when a victory for Brook would send shock waves around the world of adoring Golovkin fans.