Definitely my favorite physicist for the same reason you state. The notion that he just went around different fields and said “here’s how math can improve things,” invented some new approach, and moved on to another field to do it all over again just cracks me up.
Nowadays we'd call that "engineer's disease". I wonder how many potential Von Neumanns were discouraged from branching out into other fields by jealous gatekeepers who assume that any interest in their field by "outsiders", especially technical people, is "epistemic trespassing".
Mandelbrot did this too, but he created a lot of animosity in the process because he could be really abrasive.