Siebel Systems founder Tom Siebel, a cousin of Gov. Gavin Newsom's wife, is supporting two of the governor's biggest critics, San Jose Mayor Matt Mahan and Republican former Fox News Host Steve Hilton. Siebel sold Siebel Systems to Oracle in 2006 for approximately $5.8 billion, making him a billionaire with an estimated net worth of around $4 billion. This isn't the first time Siebel has clashed with his cousins; he also contributed $1 million to the campaign against Prop.