Well, the most talked about king... That probably depends on where you live. Henry VIII is surely a well known ruler, but I'm not sure if he's the most talked about here in Belgium. Charles V and Philip II of Spain are probably spoken as much about as Henry, maybe even more.

Anyway, to answer why he's so well known. First of all the tales of his many wives and how he got rid of them keep on startling people. He also broke with the Roman Catholic Church (related to his having many wives), which is a major event in English history. And through his daughter Elisabeth, Scotland and England would later on be united when James I / VI became king of England, which also is a major event in British history.