David Koch, billionaire conservative activist, is dead at age 79, his brother announced Friday.

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

David Koch has died, his brother confirms in a statement. pic.twitter.com/FlsC9cgThh — Kaitlan Collins (@kaitlancollins) August 23, 2019

David Koch stepped down from the brothers’ business and political network in June 2018 due to his deteriorating health.

Per NBC News, their organization has spent more than $1 billion in recent elections to bolster conservative candidates who adhere to libertarian policies.