WASHINGTON: David Koch, a billionaire American libertarian and influential donor to conservative causes, has died at age 79 after a long battle with cancer, his brother Charles said Friday.

Koch retired last year as executive vice president of Koch Industries, the conglomerate he co-owned with Charles, his older brother, and built into the second largest family-owned company in the United States.

"We wish for all to celebrate the life and impact of this most generous and kind man," Charles Koch said in a statement.

"He believed he had a responsibility to a world that had given him so many opportunities to succeed."

Both brothers were a force behind the scenes in Republican politics, giving heavily to candidates and causes that matched their conservative economic positions.

But David was socially liberal -- a supporter of abortion rights and same sex marriage as well as a non-interventionist foreign policy.

Both brothers were recognized in 2015 for bipartisan work on prison reform in the United States.

David ran as the Libertarian Party's vice presidential candidate in 1980, but later broke with it and joined forces with the Republicans.

He was remembered as an important financial contributor to cultural organizations and medical research.

He was diagnosed with advanced prostate cancer 27 years ago but through "a combination of brilliant doctors, state-of-the-art medications and his own stubbornness kept the cancer at bay," Charles said.

Born in Wichita, Kansas, Koch studied chemical engineering at the Massachusetts Institute of Technology before joining Koch Industries.

Forbes estimated his wealth at the end of his life at $42.4 billion, making him one of the world's richest persons. —AFP