For me, it would be a spiritual leader - in essence a religious leader - who could awaken the true spirits of the English people that are now enslaved and confined by the nihilistic mass choice to live according to mass media-enforced secular Leftism.
I don't think any kind of genius scientist, mathematician, engineer, artist, poet, economist, lawyer, politician (etc)- would (even if recognized and taken notice of, which seems unlikely) do more than perpetuate (and probably exacerbate - by their work being misapplied) current problems.
So what kind of person? Ideally some multi-faceted genius who is also a patriotic leader; someone like King Alfred the Great (849-899 AD). That is probably way too much to ask, since there are few if any other men in history who combine political, military, legal and scholarly ability as he did.
But that is the kind of person we need; and it is not clear to me that anybody much less wide-ranging than Alfred would suffice to inspire, encourage and mobilize a crushed and craven people with the right spirit, and get them aiming in the right direction.