LeBron James has agreed what is believed to be the single largest endorsement guarantee in history with Nike - a blockbuster deal that will ensure he represents the sports company for life.

James, a two-time NBA champion, has been a Nike athlete ever since he turned professional in 2003 - agreeing an initial seven-year deal with the Oregon company that was subsequently extended for another nine years in 2010.

Since then the company has worked with the athlete to release a line of shoes and other products bearing his name, and have now decided to ensure the relationship is a permanent one.

Financial details of the deal were not disclosed, but sources told ESPN that the figures dwarf the 10-year, $300 million deal that Oklahoma City Thunder forward Kevin Durant signed with the sports company in 2014.

"We can confirm that we have agreed to a lifetime relationship with LeBron that provides significant value to our business, brand and shareholders," Nike said in a statement.

"We have already built a strong LeBron business over the past 12 years, and we see the potential for this to continue to grow throughout his playing career and beyond."

While Nike have grown their business in part on their endorsement deals with the top stars in various sporting fields - the likes of Tiger Woods, Roger Federer and Cristiano Ronaldo are all signed to the company - James's deal is believed to be the first of its kind in its history.

"I'm very humble, man," James told reporters.

"It's been an unbelievable time for myself and my family, and I'm just grateful that Nike and [Nike founder] Phil Knight and everyone over there just believed in a skinny 18-year-old kid from Akron, Ohio, and I'm happy to be a part of such a great company."

Such an arrangement is not entirely new to the industry - Adidas is believed to have similarly long-term deals with former footballer David Beckham and basketball star Derrick Rose, while Reebok famously agreed a lifetime deal with Allen Iverson - but it is not believed Nike have adopted such a strategy before.

The risk, as Adidas seem to be learning with Rose and Reebok discovered with Iverson, is that injury or other issues can diminish a player's value over time - but Nike clearly do not feel there are such risks with James.

Six-time NBA champion Michael Jordan, in many ways Nike's blueprint for their relationship with James, is assumed to be tied to the company for good - Jordan has his own Air Jordan brand, with its established market presence, that makes more than $2bn a year for the company - but the arrangement is not believed to be formally contracted.

Nike have released 13 shoes under the James signature in recent years, with 2015 sales of his sneakers and other branded gear believed to top $400m. The 30-year-old suggested that the possibility of spinning off his own brand, similar to Jordan, had been discussed in negotiations.

"We've done a great job of building my brand to this point here today," James said. "We want to just continue it. If it makes sense for us to have a 'Team LeBron,' or whatever the name will be, we'll take a look at it and we'll go from there."

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