The 1976 contract that established Apple as a corporation sold at auction on Tuesday for $1.59 million (£1.03m), about 10 times its estimate.
The contract was drawn up by Ronald Wayne, who, along with Steve Jobs and Steve Wozniak, are listed as the three founding members of Apple. Wayne left the company after just 11 days. A document confirming his departure was also sold in the same auction lot.
Eduardo Cisneros, CEO of Cisneros Corp, bought the documents after the auction price was driven up by six keen bidders via telephone and online, forcing the price way up from the $150,000 estimate Sotheby's had put on the lot.
The contract states that Jobs and Wozniak each had 45 per cent of the new company and Wayne had 10 per cent; Wayne sold his stake in the company for just $800 (£500), but today it would have been worth nearly $3 billion.
At the time, Wayne worked as an engineer at the computer firm Atari and had previously started a slot machine company. Owning a 10 per cent stake in Apple made Wayne a tie-breaker if Jobs and Wozniak disagreed over something.
Together with Jobs, Wayne convinced Wozniak that the circuits he was producing in his day job at Hewlett-Packard could be useful to Apple. Wayne said: "Jobs and I realized that these circuits would be the core of Apple. We spent two hours in a roundtable discussion at my apartment and I was able to get Woz to accept this."
"This is a foundation document in terms of financial history, social history and technological history. It is the founding document of the company that has revolutionised technology, business, personal computing and the world," said Richard Austin, head of books and manuscripts at Sotheby's.
As documented in the Steve Jobs biography, Wayne went on to live in a small house, live off his Social Security and play the penny slot machines. He later said he had no regrets: "I made the best decision for me at the time. Both of them were real whirlwinds and I knew my stomach and it wasn't ready for such a ride."