Jobs, who has suffered from pancreatic cancer and endured a liver transplant, is an Apple co-founder and is credited with revitalizing the company in the mid-1990s.
He has been famously guarded about his health, but concerns about his illness have dogged the brand in recent years, with each leave of absence stirring fears among investors that the company will be unable to perform to its usual caliber without him. The announcement of his latest medical leave has thrust his health into the spotlight again.
Here are five things to know about the health of the Apple CEO.
1. He'd rather talk about something else. Jobs has been fiercely private about his ailments, often leaving observers -- and investors -- with little more than speculation about his health. In 2009, when Apple announced that Jobs had undergone a liver transplant, the CEO seemed to bristle at the suggestion that his health battles should be public. "Unfortunately, the curiosity over my personal health continues to be a distraction not only for me and my family, but everyone else at Apple as well," he wrote in an e-mail to his employees.
2. He was diagnosed with pancreatic cancer in 2003 ... and beat it. In 2005, Jobs said he had battled pancreatic cancer the year before and was in remission. "No one wants to die," he said in a commencement address at Stanford University. But, he said, "I had the surgery, and I'm fine now." He said he was diagnosed with an islet cell neuroendocrine tumor, a rare but treatable and less deadly form of pancreatic cancer, which usually results in death relatively quickly.
3. He underwent a liver transplant in 2009. Jobs had not made a public appearance for months when he finally stepped out in September 2009 to unveil a new line of iPods and revealed that he had undergone a liver transplant as well. "As some of you know, five months ago I had a liver transplant," he said. "I now have the liver of a mid-20s person who died in a car crash and was generous enough to donate their organs. I wouldn't be here without such generosity, so I hope all of us can be as generous and elect to be organ donors."
4. ... And attributed his sudden weight loss in 2008 to a "nutritional problem."
Jobs' extreme weight loss in 2008 left him looking gaunt and raised fears that his cancer had returned. But Jobs said his cancer remained in remission. He said he was suffering from a "nutritional problem" and had already begun to feel better. "My doctors think they have found the cause -- a hormone imbalance that has been robbing me of the proteins my body needs to be healthy," he said in early 2009. "The remedy for this nutritional problem is relatively simple and straightforward, and I've already begun treatment."
Just days later, however, Jobs announced that he would be taking a medical leave. "During the past week I have learned that my health-related issues are more complex than I originally thought," he wrote in a letter to Apple employees. "In order to take myself out of the limelight and focus on my health, and to allow everyone at Apple to focus on delivering extraordinary products, I have decided to take a medical leave of absence."