Richard Feynman (1918-1988) was an American physicist.
Feynman's major contribution was to quantum electrodynamics. He introduced the diagrams, now called Feynman diagrams, which are used to describe the behaviour of systems of interacting particles. He was awarded a Nobel Prize for Physics in 1965.
Feynman liked to tell a story about how when he was a little kid, he asked his father, "Why do things fall?" As an adult, he praised his father for answering, "Nobody knows why things fall. It's a deep mystery, and the smartest people in the world don't know the basic reason for it." Contrast that with the average person's off-the-cuff answer, "Oh, it's because of gravity." Feynman liked his father's answer, because his father realized that simply giving a name to something didn't mean that you understood it. 
Feynman cut through the red tape and figured out what caused the Challenger disaster.
- I took this stuff that I got out of your seal and I put it in ice water, and I discovered that when you put some pressure on it for a while and then undo it, it doesn't stretch back. It stays the same dimension. In other words, for a few seconds at least and more seconds than that, there is no resilience in this particular material when it is at a temperature of 32 degrees.
His style of investigating with his own direct methods rather than following the commission schedule put him at odds with Rogers, who once commented, "Feynman is becoming a real pain." During a televised hearing, Feynman famously demonstrated how the O-rings became less resilient and subject to seal failures at ice-cold temperatures by immersing a sample of the material in a glass of ice water.
Feynman was so critical of flaws in NASA's "safety culture" that he threatened to remove his name from the report unless it included his personal observations on the reliability of the shuttle. He argued that the estimates of reliability offered by NASA management were wildly unrealistic, differing as much as a thousandfold from the estimates of working engineers. "For a successful technology," he concluded, "reality must take precedence over public relations, for nature cannot be fooled."
- NASA officials argue that ... since the Shuttle is a manned vehicle "the probability of mission success is necessarily very close to 1.0." It is not very clear what this phrase means. Does it mean it is close to 1 or that it ought to be close to 1? 
- Surely You're Joking, Mr. Feynman! - his personal and academic life up to the 1960s
- What Do You Care What Other People Think? - half the book is about the Challenger disaster
- Gleick, James (1988-02-17). Richard Feynman Dead at 69; Leading Theoretical Physicist. New York Times. Retrieved on 2007-01-28.
- Feynman, Richard P. (1986) http://history.nasa.gov/rogersrep/v2appf.htm Appendix F - Personal Observations on Reliability of Shuttle]