Billionaire Thomas Tull is looking to invest in AI startups to give the US a technological edge over China. He has already taken a stake in a firm that enables drone swarms to operate autonomously and is looking to raise up to $5 billion for a fund to back defense-focused firms. Tull has a net worth of about $3 billion and is a serial entrepreneur with a minority stake in the NFL’s Pittsburgh Steelers and a 4,000-acre ranch in Idaho.