Silicon Valley billionaire Tom Siebel says he's recovering from broken ribs and legs after an elephant charged at him and a tour guide in the Serengeti National Park in Tanzania a month ago. The 56-year-old Siebel told the San Jose Mercury News that while on safari on August 1, the animal plowed into the guide and then attacked him, breaking several ribs, goring him in the left leg and crushing his right leg. He says he and the guide were watching a group of elephants from about 200 yards away when one animal charged at them without warning. "There was no apparent reason, nothing that should have made it feel threatened," Siebel says. "It was quiet, and then the quiet stopped." He has been in a wheelchair but says he expects to make a full recovery after reconstructive surgery and physical therapy. Siebel's estimated worth is US$1.9 billion as of 2008. His wealth rocketed in 2006 when he sold his database company, Siebel Systems, to Oracle for billions. Before founding Siebel Systems, Siebel worked as an executive at Oracle between 1984 and 1990. He now invests his assets though a holding company, First Virtual Group, and in 2008 was ranked among BusinessWeek's 50 most generous US philanthropists.