Google cofounder Sergey Brin and John Doerr have donated a combined $94 million to undercut California's proposed billionaire tax. Peter Thiel has donated $3 million to a separate group. Getty Images A handful of California's estimated 214 billionaires are trying to stop a proposed wealth tax. Google cofounder Sergey Brin, who moved assets out of the state, has spent $82 million. Here are those joining him, including Peter Thiel, ex-Google CEO Eric Schmidt, and DoorDash CEO Tony Xu. California