That is far from the only thing he did. He was the wunderkind of the project, and he did all kinds of things.

See for instance Gleick's Feynman biography, "Genius".

http://www.goodreads.com/book/show/98685.Genius

Another good read about the project is this bio: "The Curve of Binding Energy: A Journey into the Awesome and Alarming World of Theodore B. Taylor"

...which is obviously mostly about Taylor (on the Manhattan Project), but has some Feynman anecdotes.

http://www.goodreads.com/book/show/54968.The_Curve_of_Bindin...