Who are some underrated people in history?
I will not say Jesus because he is a person of faith, for me, more than a person of history. But …

Gotthold Ephraim Lessing (1729–1781) and his ditch (der garstige breite Graben) is highly underrated. Good insight into epistemology! And into faith. Only Kierkegaard, methinks, gives an answer.
In religion, St Mary of Egypt – penitence without the institution.
And maybe me!?