Billionaire David Koch, who along with his older brother was a formidable conservative activist and donor for decades, died Friday morning at age 79.

"It is with a heavy heart that I announce the passing of my brother David," Charles Koch said in a statement Friday. "Anyone who worked with David surely experienced his giant personality and passion for life."

"While this is a very sad day for us all, I want you to know that David was proud of the extraordinary work you all have done to make Koch Industries the successful company that it is today. He will be greatly missed, but never forgotten," Charles Koch added.

David Koch had stepped down from Koch Industries just over a year ago for health reasons.

He was diagnosed with prostate cancer more than two decades ago and had been involved in donations to numerous cancer research charities and medical groups.

When he stepped down from Koch Industries, Charles Koch told reporters that "issues have not been resolved and his health has continued to deteriorate."

"As a result, he is unable to be involved in business and other organizational activities," Charles Koch said last year.

The Koch family has been known largely for its massive political contributions to Republican candidates and libertarian-leaning causes.

Together, Charles and David were credited with helping finance the Tea Party movement that assisted Republicans in reclaiming the House in 2010.

David Koch was a prolific supporter of GOP candidates, though he did not back President Trump's campaign in 2016. He vocally supported the Republican tax-cut plan in and previously served as the Libertarian Party's candidate for vice president in 1980.