David H. Koch, the billionaire industrialist who combined his vast wealth and libertarian-tinged brand of conservatism to influence candidates and campaigns at all levels of American politics, is stepping away from his political and business interests because of declining health, his company announced Tuesday.

[David Koch Died on Aug. 23 at the Age of 79]

Mr. Koch’s brother Charles said in a letter to employees at Koch Industries, the company the two controlled, that David Koch’s health problems had made it impossible for him to continue working. “Unfortunately these issues have not been resolved and his health has continued to deteriorate,” the letter said. “We are deeply saddened by this.”

The Koch family has been influential in conservative politics for generations, long before its name became synonymous with big money in the Republican Party. David Koch, in fact, was the vice-presidential nominee for the Libertarian Party in 1980. Fred Koch, the family patriarch and father of Charles and David, who founded Koch Industries, was a founding member of the far-right, anti-Communist John Birch Society.

With millions of dollars in donations over the years, the Kochs’ contribution to today’s Republican Party has been seminal, helping to solidify doctrine that favored businesses and worked against stricter environmental regulations. Now, the absence of David Koch, 78, who was the more public and political of the brothers, will inevitably raise questions about whether the Kochs’ mission will shift further toward nonpolitical endeavors.