I am not 100% positive, but I believe that he had pancreatic cancer, which is very tough to beat, esp. if you have a rare form of it. When I saw that picture of him that was released just after he announced that he was leaving Apple, I knew the poor guy was in trouble.
I loved to hate Apple, but I always admired and respected their stability, growth, and products. I knew Steve was brilliant. When I learned and saw how ill he looked, I toned it down. I had no idea.
You know how we choose sides; Ford vs. Chevy--Honda vs. Toyota--Microsoft vs. Apple, etc. It was all in good stubborn fun. I know Steve liked to participate in that too. He was proud, and rightfully so.