"In 1944, E. Onsager produced, quite unexpectedly, an exact evaluation of the partition function of the model in two dimensions. It was a real tour de force. I had studied his paper in Chicago in the spring of 1947, but did not understand the method, which was very, very complicated, with many algebraic somersaults... I was thus led to a long calculation, the longest in my career. Full of local, tactical tricks, the calculation proceeded by twists and turns. There were many obstructions. But always, after a few days, a new trick was somehow found that pointed to a new path... after about six months of work off and on, all the pieces suddenly fitted together, producing miraculous cancellations, and I was staring at the amazingly simple final result[, the spontaneous magnetization of the ising model.]"