In a stunning change for one of Silicon Valley's most legendary corporations, Larry Ellison, who for 37 years steered Oracle to become one of the world's biggest and well known technology companies, is giving up his position as CEO to become executive chairman and chief technology officer. The Redwood City corporation's board promoted both co-presidents Safra Catz and Mark Hurd as co-CEOs to replace Ellison, who turned 70 in August.