In 2004, Cook became the CEO of Apple because Steve Jobs went for his pancreatic cancer surgery.
After 5 years, in 2009 he again became the CEO for several months while Steve Jobs was away for his liver transplant.
In January 2011, he was made the CEO of Apple the third time when the Apple’s Board of Directors granted a leave to Steve Jobs.
During that time, Tim Cook will be responsible for most of the apple’s day-to-day operations while CEO Steve Jobs still makes the major decisions.
tim cook