Jim Sinegal and Jeff Brotman first dreamed up the idea for Costco Wholesale in 1982. The late Brotman was an attorney, who was inspired to open a European-style wholesaler after taking a trip to France.
Brotman told CNN in 2009 that he ended up cold-calling Sinegal, and the two hit it off.
Sinegal was a retail executive who'd previously worked under businessman Sol Price at a warehouse club called Fedmart.
Price had founded his own chain, Price Club, on July 12, 1976, in San Diego. Price Club exclusively offered memberships to small business owners.
Sinegal and Brotman later told CNN that they planned to essentially "clone Price Club" when they launched the first-ever Costco in Seattle in 1983.
Years later, Price Club and Costco would merge to become the Costco we all know and love today.
But the first warehouse bearing the Costco name kicked off their grand opening with a business show on Sept. 15, 1983.
Back when it first opened its doors, Costco offered business owners memberships for a $25 annual fee.
Meanwhile, "Group Gold" Costco members could shell out $30 a year to gain access to the warehouse chain.
Sinegal told Motley Fool that the chain's first 100,000 square foot warehouse was a "pretty simple facility" that lacked "many of the enhancements that we've added to the business since then."
In 2009, he also told CNN that the "crowds weren't overwhelming" at first, but "business built up" gradually. Sinegal would go on to serve as Costco's CEO from 1983 to his retirement in 2011.
Costco's low-priced, bulk-sized offerings ended up catching on with shoppers.
Less than a year after it was founded, Costco began to expand across the Pacific Northwest ...
... launching stores in Portland, Oregon, and Spokane, Washington, in 1983.
Sinegal explained the chain's rapid expansion to the Los Angeles Times in 1985, saying, "We are working to get established in certain markets, to preempt those markets."
The emergence of Sam's Club, Walmart's answer to the influx of members-only warehouse clubs, also spurred further expansion.
"When Walmart announced it was going into the discount warehouse business, we had to compete and grow quickly," Brotman told CNN in 2009.
"That's why we expanded as fast as we did," the Costco co-founder said.
By the end of 1984, 200,000 Americans had become Costco members.
That same year, The Associated Press dubbed both Price Club and Costco as "key players" in the wholesale retail game.
Costco filed for an IPO on Dec. 5, 1985, according to the company's website. Price Club had already gone public back in 1980.
Investopedia calculated that anyone who bought 100 shares of Costco — at $10 a pop — would have made $138,768 by Dec. 1, 2018.
Just three years after opening its doors, Costco was a $1 billion company, Sinegal told CNN.
At that point, the chain boasted "17 locations, 1.3 million members, and 3,740 employees," according to Costco's website.
Costco and Price Club would ultimately merge in 1993. Initially, the new company went by PriceCostco, only to ultimately switch to the name Costco Companies Inc. in 1997.
A former employee who started at Price Club in 1984 and stayed with the company for 20 years told Business Insider that, initially after the merger, there was a slight divide between "red" Costco warehouses and "blue" Price Club warehouses.
"When I was a corporate auditor for the company, the first thing the folks at the warehouse would ask me is, 'Are you red or blue?'" he said.
But he added that ultimately, employees got on the same page. "It wasn't really a bad thing," the former employee said. "Price Club had evolved into a different animal and Costco really took us back to bare bones."