The prototype has a battle-weary expression, later modified

GI Joe was the vision of Don Levine, a Korean War veteran and former Hasbro executive.

He set out to develop a toy that would do for boys what rival Mattel's Barbie had done for girls.

Introducing boys to dolls - renamed action figures - proved a lucrative concept, a "razor-razor blade strategy," according to its creator. He realised the vast marketing potential of the soldier and his myriad accessories.

Today, 375 million GI Joe sales later, the name is recognised in 85% of US households. It was inspired by the 1945 movie Story of GI Joe, starring Burgess Meredith and Robert Mitchum.

For decades, the foot-high prototype of Joe lay in a cardboard box in Mr Levine's Rhode Island home.

Mr Levine, 75, said it was simply time to sell the prototype - and other early Joes - and divide the proceeds among his children and grandchildren.

'Blank stare'

"He was such a unique toy concept," Derryl DePriest, a 38-year-old Hasbro marketing director who personally owns thousands of GI Joes, told Associated Press news agency.

Toy expert John Petty said Joe's price would far surpass Barbie sales

"It required completely rethinking how boys would play with toys and really taking a chance."

Levine and his design team laboured to make the first figure and his gear, seeking a look that represented no soldier in particular and authenticity in his helmet and fatigues.

Toy experts say the figure that went into production had a more serene expression than the battle-weary look of the prototype.

John Petty, auction director for Heritage Comics - organising the sale in San Diego - said the eventual choice of face was "brilliant, because it is a blank stare".

"There's no expression there. Whatever you wanted him to be feeling, you could put that there," Mr Petty told AP.