A high-stakes clash between two of the world’s most influential billionaires is playing out in public, as Elon Musk and Bill Gates exchange barbs over foreign aid policy and humanitarian fallout.

Tesla CEO Elon Musk has long captured attention with his big promises, from the Hyperloop high-speed transportation system Musk claimed would revolutionize the way we travel to a recent comment about how Tesla owners can one day make money with their autonomously driven cars,

The Microsoft co-founder and philanthropist condemned his fellow billionaire for overseeing deep cuts to the U.S. Agency for International Development in the Trump administration.