Cromwell himself would be a good subject for an unflinching drama, there’s a lot going on with that guy.
On a wider topic, the First Crusade and its aftermath offers a very rich tapestry of religious fanatacism, mercenary self interest, political chicanery, terrible violence, very occasional outbreaks of humanity.
Practically any episode of British Imperial history deserves a long hard look, I’m going to propose as options 1) the Malay Emergency and 2) the post-slavery ban missionary led incursions into Africa, because seeing hypocrites skewered is always fun.
Back on biography, would be interested to see treatments of the lives of Teddy Roosevelt, Otto von Bismark, Florence Nightingale, Empress Cixi and Newton/Leibniz