Apple Chief Executive Officer Steve Jobs shocked the world again Wednesday, this time with his sudden resignation, and the board of directors announced that Chief Operating Officer Tim Cook will replace him. Cook has been filling in for Jobs since he took medical leave in January. The Alabama native, 50, joined Apple in 1998, first to oversee the manufacturing of Apple’s computers. An industrial engineer by trade, he also has a master’s degree from Duke University in business administration. Prior to coming to Apple, he worked at IBM and Compaq, the computer company now owned by Hewlett-Packard. Cook took over for Jobs for two months in 2004 while Jobs recovered from surgery to remove a tumor from his pancreas. Cook was appointed Apple COO in 2005, and filled in as CEO again during Jobs’s second medical leave in 2009.