Cromwell (1485?-1540) was Secretary to King Henry VIII of England. He was the king’s fixer, his chief factotum, the guy who got things done. Cromwell got some quite tremendous things done: the annulment against Papal opposition of Henry’s first marriage, the separation of the English Church from Rome, the dissolution of the monasteries, and the framing (probably) and execution of Henry’s second wife, Ann Boleyn.
Ban jun ru ban hu goes the old Chinese saying: “To attend a prince is to attend a tiger.” Cromwell’s religious radicalism was too much for the king at last, and he lost his head.
Mantel doesn't actually remove Cromwell's head until the third book of her trilogy, not yet published.
The story of Henry, his wives, and his religion, has often been told, but never before (so far as I know) through Cromwell's eyes. In fiction about the Tudors—starting with Shakespeare—he is mostly a nonentity, a hack administrator enforcing Henry's edicts.
Alison Weir's fine biography of Henry has an appendix giving the author's opinions about the many portrayals of Henry on film. From which:
For me, as a historian, the finest and most accurate portrayal of Henry VIII was that by Keith Michell in the BBC TV series of six plays, The Six Wives of Henry VIII (1970).
As a non-historian, I'm glad to know my own impressions have scholarly support. For people of my generation, Michell was Henry. The way he aged through that series was a masterpiece of makeupry.
Not much I have since read about Henry contradicts Michell's portrayal; though it seems clear that contra the BBC show, Henry did successfully get the leg over with Katherine Howard.
The best song about Henry is of course this one.