This topic seems to come up at least once a year.
My standard answer has always been, and still is: the life of Alexander Hamilton. His contributions to America, and his sheer genius, have been mostly forgotten.
I would also add, for being horrendously under-appreciated, Rosalind Franklin. Her largely-ignored contributions to science were astounding and her tragically short life seems, to me, anyway, ready-made fodder for any movie.