David Koch, the 78-year-old billionaire businessman and prominent supporter of the Republican Party, announced on Tuesday that he would be stepping down from his role as Vice President of Koch Industries, a company that “operates refineries and manufactures paper towels, carpets and many other products.” A memo sent by the company’s Chairman and CEO, Charles Koch, said that Koch was retiring due to his deteriorating health. The Wall Street Journal reports that the memo also mentioned that Koch had been hospitalized for an undisclosed condition back in 2015.

According to The Chicago Tribune, Charles Koch still plans to stay on as CEO of Koch Industries and will become the new face of the company’s political efforts.

David Koch and his brother, Charles, have been controversial figures both in the business world and the political realm. They have been especially active in GOP politics; the Journal says that the brothers used the fortune to reshape Republican politics completely. Koch also gave very generously to conservative organizations and philanthropic donors. As such, the Democrats had vilified Koch and his brother relentlessly over the past decade, with Former Senate Majority Leader Harry Reid accusing the GOP of having a “Koch addiction.”

Amidst their steadfast support of the Republican Party, the Koch brothers have been incredibly outspoken in their opposition to President Trump. They did not contribute any money to Trump’s campaign and have expressed strong support for protecting DACA recipients. In fact, CNBC reports that Dave Koch’s retirement comes a day after the Koch-backed political network announced a multimillion-dollar campaign against Trump’s tariffs.