In his book Surely You're Joking, Mr. Feynman!, Feynman himself says that he did not know how to compute contour integrals. To give a direct quote, he says:
One thing I never did learn was contour integration.
I find this fascinating as there is a famous result in quantum field theory involving contour integration that is named after Feynman (the Feynman propagator).
Was Feynman the first to derive the Feynman propagator? If so, how did he do it if he supposedly did not know about complex contour integration. If not, why is it named after him?