Billionaire industrialist David Koch, a driving force behind conglomerate Koch Industries who as one of the world’s richest people became a major financier of conservative causes and political candidates, has died at age 79, his brother said on Friday.

Charles Koch, Koch Industries Inc’s chairman, disclosed the death in a statement that touched on his younger brother’s lengthy battle with prostate cancer and his philanthropic contributions to medical research, education and the arts.

“He will be greatly missed, but never forgotten,” Koch said in a statement addressed to employees. “David was proud of the extraordinary work you all have done to make Koch Industries the successful company that it is today.”

Koch, a philanthropist and patron of cultural and medical institutions, amassed his vast wealth with a large ownership stake in Koch Industries, the Wichita, Kansas-based company he ran with Charles.

With Charles as chairman and chief executive and David as executive vice president, Koch Industries - one of the world’s largest privately held businesses - aggressively expanded beyond the oil refining business their father created into an array of new ventures.

David Koch stepped down from the business and political activities in June 2018, citing declining health.