I was reading the other day about Hengist and Horsa and beyond from Anglo-Saxon history/pseudo-history and came across a term (now forgotten) whereby some believe that the ancient gods of the Germanic and Scandinavian mythology were once great men/women who had ascended to godhood, just wanted to know if anyone knew this term
Are you maybe thinking of 'Euhemerism'? That would be the idea that Mythology is based on the actions of mortal men and women, which have been deified through retellings or through lack of understanding.
If that's the one I could expand based on Old Norse sources.