George Siemon, the co-founder and longtime chief executive of Organic Valley, announced this week he is leaving the company he helped build over the last 30 years.

Under Siemon’s leadership, Organic Valley, based in La Farge, Wis., became the largest farmer-owned organic cooperative, and one of the largest organic brands, in the United States. Siemon is a leading national figure in advocating for independence from corporations, stringent organic standards and support for farm families.

“Our job is not to increase our own profits, it’s to do organics right,” Siemon told the Star Tribune in a 2016 interview.

Siemon appeared as the face of Organic Valley as recently as last week when he could be found lingering around the company’s exhibition booth at Natural Products Expo West, the nation’s largest gathering for natural and organic food makers.

The company did not offer a reason for his departure and company spokeswoman Elizabeth McMullen did not return multiple requests for comment. Organic Valley’s board of directors appointed Bob Kirchoff, chief business officer, as interim CEO.

“We are indebted to George for his 30 years of service to Organic Valley, for saving countless families, and for creating a path for generations more to stay on their farms in the process,” said Organic Valley Board Chairman Arnie Trussoni, in a statement posted to the company’s website.

Siemon was one of seven farmers in the La Crosse, Wis., area who started the organization in 1988 as a way to save their family farms, and use better land management practices, at a time when agribusiness was gobbling up farmland across the Midwest.

“What Organic Valley really represents to me, and to many, many people who grew up in the industry, is the true blue North Star of the industry,” said John Foraker, former CEO of Annie’s and co-founder of Once Upon a Farm organic baby food. “George is just really revered. He always thought for the long term, which is so different from business now that is so focused on short-term returns.”

During his tenure, the organic industry boomed and Organic Valley grew into a $1 billion business. More recently, however, the company has been coping with an oversupply in egg and dairy pools that has depressed the market. In 2017, the co-op lost money for the first time in 20 years.

“We have experienced many cycles in our history, but this has been the worst one,” Siemon wrote in the company’s most recent annual report. “2017 was a turning point where we could see our future as one where organic is becoming commodified. This will be threatening for much of our success. Our strategy is not to accept that.”

There are more than 2,000 farms in the co-op, spanning 36 states and Canada, Australia and the United Kingdom.