I see the Kwisatz Haderach as the combination of all the mental disciplines used throughout the Imperium. Muad'Dib had the prana-bindu training of the Bene Gesserit. He was also a Truthsayer. He had the prescience of a Guild Navigator and the intellectual capabilities of a Mentat. He also had the Other Memory of a Reverend Mother, and was the Fremen lisan al-Gaib (the "Voice From the Outer World"). Muad'Dib was the culmination of all these disciplines.

There are a few other characters in the Dune novels I think either actual Kwisatz Haderachs, or at least, good candidates: