Clayton Christensen, 58, is one of the most influential business theorists of the last 50 years. The Harvard Business School professor's 1997 book, The Innovator's Dilemma, introduced in elegant terms the notion of "disruptive innovation." One industry that always eluded Christensen's influence was healthcare. Caregivers and insurers told him his theories didn't apply to their complex industry. Christensen knew they were wrong. His investigation culminated in his 2009 book, The Innovator's Prescription, written with two doctors. It exposed the many ways health care was broken and recommended numerous ways it can be systematized and disrupted the same way mainframes gave way to PCs and now iPhones. Christensen's work took on new urgency the past few years as he suffered a heart attack followed by cancer followed by a stroke. For Christensen it was not a reason to get too upset. It was another opportunity, in a lifetime full of them, to gain insight into how to make the world work better.