Steve Jobs Photos: Before and After Medical Mystery

(CBS) What's wrong with Steve Jobs?

The Apple CEO has been battling health issues and rumors for some time. This morning, the 55-year-old technology pioneer told his company he was taking time to get his health back in order.

"At my request, the board of directors has granted me a medical leave of absence so I can focus on my health," said a Jobs' email to his Apple staffers, according to Business Insider.  "I will continue as CEO and be involved in major strategic decisions for the company."

Over the years, Apple watchers have seen Steve Jobs transform from a fairly pudgy frame in the 1990s to an almost skeletal visage in the last few years. Jobs has never been very forthcoming with details.

Here's a timeline of what we do know based on his own statements.

2004: Jobs had a cancerous tumor removed from his pancreas. Pancreatic cancer is usually terminal within a few years, but Jobs said he had a rare form, islet cell neuroendocrine tumor, which has a far better success rate. He said he did not require chemotherapy or radiation.

2009: Jobs took a 6-month leave of absence to address, what he called a hormone imbalance that had "been 'robbing' me of the proteins my body needs to be healthy. He said that was too blame for his extremely gaunt appearance.

2009: Jobs underwent a liver transplant at Methodist University Hospital Transplant Institute in Memphis, Tenn. A hospital press release called him the "sickest patient on the waiting list at the time a donor organ became available."

2011: Jobs takes a leave of absence to restore his health. Cause unknown.