Apple Chief Executive Officer Steve Jobs shocked the world again Wednesday, this time with his sudden resignation, and the Board of Directors announced shortly afterward that Chief Operating Officer Tim Cook, who has been filling in for Jobs since he took medical leave in January, will replace him. Who is Tim Cook? The Alabama native, 50, joined Apple in 1998, first to oversee the manufacturing of Apple computers. An industrial engineer by trade, Cook 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 HP. 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 as the CEO again during Jobs’s second medical leave in 2009.