“There are two types of genius. Ordinary geniuses do great things, but they leave you room to believe that you could do the same if only you worked hard enough. Then there are magicians, and you can have no idea how they do it. Feynman was a magician.”
Hands Bethe, Theoretical physicist and Nobel laureate.

Richard P. Feynman (May 11, 1918 – February 15, 1988) was an American theoretical physicist, a laureate of the Nobel Prize in Physics (1965) and inventor of Feynman diagrams, introduced in 1948 and still widely used today in studies of collisions and scattering of elementary particles.

Five particular achievements of Feynman were crucial to the development of modern physics (according to Encyclopedia Britannica):

First, and most important, is his work in correcting the inaccuracies of earlier formulations of quantum electrodynamics, the theory that explains the interactions between electromagnetic radiation (photons) and charged subatomic particles such as electrons and positrons (antielectrons).

Second, he introduced simple diagrams, now called Feynman diagrams, that are easily visualized graphic analogues of the complicated mathematical expressions needed to describe the behavior of systems of interacting particles. This work greatly simplified some of the calculations used to observe and predict such interactions.

Feynman diagram of electron-positron annihilation

Feynman provided a quantum-mechanical explanation for Lev D. Landau’s theory of superfluidity — i.e., the strange, frictionless behavior of liquid helium at temperatures near absolute zero.

Feynman and Murray Gell-Mann devised a theory that accounted for most of the phenomena associated with the weak force, which is the force at work in radioactive decay. Their theory, which turns on the asymmetrical “handedness” of particle spin, proved particularly fruitful in modern particle physics.

And finally, while working with experimenters at the Stanford Linear Accelerator on the scattering of high-energy electrons by protons, Feynman invented a theory of “partons,” or hypothetical hard particles inside the nucleus of the atom, that helped lead to the modern understanding of quarks.

Murray Gell-Mann was reported to grumble that Feynman “spent a great deal of time and energy generating anecdotes about himself.” One of my favorite Feynman anecdotes is titled “It Sounds Greek to Me!”, from the book Surely You’re Joking Mr. Feynman:

One time, in 1957, I went to a gravity conference at the University of North Carolina. I was supposed to be an expert in a different field who looks at gravity.
I landed at the airport a day late for the conference (I couldn’t make it the first day), and I went out to where the taxis were. I said to the dispatcher, “I’d like to go to the University of North Carolina.”
“Which one do you mean,” he said, “the State University of North Carolina at Raleigh, or the University of North Carolina at Chapel Hill?”
Needless to say, I hadn’t the slightest idea. “Where are they?” I asked, figuring that one must be near the other.
“One north of here, and the other is south of here, about the same distance.”
I had nothing with me that showed which one it was, and there was nobody else going to the conference a day late like I was.
That gave me an idea. “Listen,” I said to the dispatcher. “The main meeting began yesterday, so there were a whole lot of guys going to the meeting who must have come through here yesterday. Let me describe them to you: They would have their heads kind of in the air, and they would be talking to each other ,not paying attention to where they were going, saying things to each other, like ‘G-mu-nu. G-mu-nu.’”
His face lit up. “Ah, yes,” he said. “You mean Chapel Hill!”
He called the next taxi waiting in line. “Take this man to the university at Chapel Hill.”
“Thank you,” I said, and I went to the conference.