Amazing. I always knew him as the discoverer of the Tutte Graph, which was the first known counterexample to what at the time was the most promising route to proving the Four Color Theorem:

https://en.wikipedia.org/wiki/Tutte_graph

Later I learned about the Tutte polynomial of a graph, which I believe ranks up there as one of the deepest and most unexpected relations in mathematics.

https://en.wikipedia.org/wiki/Tutte_polynomial