(Reuters) - Legendary U.S. oilman Harold Hamm, who once called the Organization of the Petroleum Exporting Countries a "toothless tiger," will step down as chief executive of Continental Resources CLR.N and become its executive chairman, the company said on Wednesday.

FILE PHOTO: Harold Hamm of Continental Resources introduces himself at a dinner for business leaders hosted by U.S. President Donald Trump at Trump National Golf Club in Bedminster, New Jersey, U.S., August 7, 2018. REUTERS/Leah Millis/File Photo

Hamm will be replaced as CEO by William Berry, a former ConocoPhillips COP.N executive and Continental board member, as of Jan. 1. Jack Stark will remain as president and also become chief operating officer.

Hamm grew up the youngest of 13 children in rural Oklahoma and started working in the oilfields as a teenager. He founded the North Dakota oil producer in 1967 at the age of 21, and his gamble on the Bakken oilfield in North Dakota and Montana made him a billionaire.

Hamm, who owns 77% of Continental, said in a statement on Wednesday that his “long history of buying, not selling” shares “will not change.”

“As for me, I’m not going anywhere,” Hamm said. “I’m an oil finder and geologist at heart.”

“He was a small producer just like the rest of us. But Harold just had a passion to find big oilfields,” said Mike Cantrell, an Oklahoma oil and gas producer who has known Hamm for 30 years. “He’s had a tremendous impact on American energy. I’d say there is no living American, perhaps with the exception of Charles Koch, that has had as much influence on the American oil and gas industry.”

Hamm famously derided OPEC as a “toothless tiger” in 2014 but in 2018 credited the cartel with helping to relieve a global supply glut. He played a key role in getting a longtime U.S. ban on oil exports lifted in late 2015, a policy change that upended global markets.

In 2015, Hamm paid his ex-wife Sue Ann Arnall $975 million in one of the largest divorce settlements in U.S. history. Arnall was a former Continental executive who had been married to Hamm for 26 years.

He was an informal campaign adviser to U.S. President Donald Trump in 2016 and was considered for a U.S. cabinet post.

Shares of Continental closed at $33.30 on Wednesday, up a fraction prior to the announcement.