The man behind Charles Martin's mission to shatter Briton Anthony Joshua's world title dream is Scouser Paul Cain, who was once Sylvester Stallone's chef.

Martin (23-0-1, 21 KOs) makes a first defence of his IBF world heavyweight title against 2012 Olympic gold medallist Joshua (15-0, 15 KOs) at London's O2 Arena on April 9.

The American's rapid rise to fame and fortune from obscurity has taken many by surprise, but not Los Angeles-based Cain, Martin's camp manager who has been with him from the start when he was part of a programme funded by U.S. TV executive Michael King to produce world boxing champions.

King died aged 67 last May and never got to see his dream become reality when Martin lifted the IBF world title after a third round TKO win over Ukrainian Vyacheslav Glazkov, who had injured a knee, in New York two months ago.

"I went over to America in 1984 for a holiday and didn't leave," said Cain, who also runs two British bars in LA. "I was a chef at the time, got a job as a chef with Sylvester Stallone and I was with him for 12 years. I became his right-hand guy.

"Through all the contacts I made by working with Sly, I met a gentleman by the name of Michael King who owned King World. I became his chef about 20 years ago and we became very close friends.

"Then Michael started up a boxing programme called All-American Heavyweights. Michael asked me to do all the food for the boxers, when I was doing the food he just kept asking me 'do you want to do this, do you want to run this department?' and within a year I was the general manager."

Paul Cain, left, has played a vital role in getting Charles Martin ready for Anthony Joshua. Andrew Redington/Getty Images

One of those on King's boxing programme, which was later named King Sports, was Carson-based southpaw Martin, who took up boxing 10 years ago.

"I was doing different things in construction at the time," Martin told reporters during a trip to London to promote the fight with Joshua. "I was in Phoenix Arizona working double shifts. I was working hard and I know the value of hard work. These are working man's hands.

"When I was doing the construction in the hot summer sun, I was out there with the hammer and nails building and it is very, very hot. I was thinking, 'this can't be it, I want to be somebody'.

"I had a lot of talent but just didn't know how to utilise it. I wasn't good at football or basketball. I didn't want to be that 6 foot, 5 inch guy stacking groceries in the market. I didn't want to be that guy that they say 'hey can you get that up there for me'.

"My first son's mom's brothers introduced me to boxing. I knew I was a leftie [southpaw] and how to throw shots. Then I got into the boxing school in California. That was a chance at life to make something. It really opened me up and I was very inspired."

After making his professional debut in 2012, Martin steadily built an unbeaten record before suddenly finding himself challenging for a version of the world title.

After Manchester's Tyson Fury produced a shock points win over Ukrainian Wladimir Klitschko, the Briton was immediately stripped of the IBF belt for agreeing an instant rematch instead of making a first defence against the IBF mandatory challenger: the winner of Glazkov versus Martin in January.

Charles Martin won the IBF world title after a third round TKO win over Vyacheslav Glazkov. AP Photo/Frank Franklin II

After King's death, Cain retained a role within unbeaten 29-year-old Martin's career and has played a vital role in getting Martin ready for Joshua.

"Michael's dream has really come to fruition," said Cain. "Everyone said he was mad, everyone said it wouldn't work. We went through 800 football and basketball players, and 6 foot, 5 inch athletic guys.

"It was around $12 million to $16m (£8.3m-£11m)we spent. His thought track was to put USA boxing back to the forefront. He was a wealthy guy and he loved boxing.

"Charles, when he arrived, had not had an amateur fight. I then played a part in doing the deal for Charles to go with Mike Borao, but it was Leon Margules who did the deal.

"King Sports is still open but I'm not part of it and Charles Martin asked me to stay with him. I was not calling the shots but I ran a lot, I organised the sparring, organised the flights, got the medicals, got the tapes ready to watch.

"Charles asked me to stay with him and we carried on as if we were still at King Sports and as if Michael is still alive. I am now his camp manager.

"Under the direction of Mike Borao, Leon Margules, the trainers Henry Tillman and Jamal Abdulah, we all sit down and talk about sparring partners, where we are going to stay, whose gym we will use and I implement a plan."

Martin will be handsomely rewarded for fighting outside of America for the first time and conceding home advantage to his British challenger: he will reportedly earn a guarantee of nearly £3.5m ($5m), which could nearly double if the fight does well on pay-per-view sales in the UK.

Martin can also be assured of a hostile reception against Joshua, who is arguably Britain's biggest boxing star, but Cain is confident the champion will be unfazed by the occasion.

"People think the flamboyance of it all at the O2 will affect Charles, but that won't bother him whatsoever," he said. "He is completely the real deal. Charles will get tested and Joshua will get tested but I think Charles will be the one that is there at the end of the fight."