Harold Godwinson is probably my favorite historical figure of all time. A man of extraordinary ability and of good character, he had acted as regent for King Edward the Confessor, who died without an heir. Harold was far and away the best choice to rule England. But there were overseas competitors who were related who wanted to job - Harold Hardrada Sigurdsons of Norway and the king of Demnark as well as Prince William of Normandy. The king of Denmark dropped out of the contest early on, but Harold Hardrada and William were both determined to become king of England and they BOTH invaded within days of each-other! Norway's Harold in the north of England first, and Godwinson had to reform his militia and marc two hundred miles north to face the old Viking. After defeating the fierce Norsemen word came to King Harold that the Normans were invading in the south. So his men marched another 200 miles in just days, with no rest, after making a 200 mile trek north and fighting a major battle, to face William and his invaders at Hastings.
And King Harold almost won. He had the Normans (actually a coalition of troops from all over Europe who came to fight for William with the promise of land in England) pinned down on the beach. In desperation William ordered the archers to shoot up into the air to get around the English shields. One arrow struck King Harold in the eye, went into his brain. But he kept fighting, although he grew weaker and weaker and eventually expired. A sad end for so able and dedicated a man.
With King Harold gone the fight went out of the English and eventually they fell for the very same trick King Harold used on Harold Hardrada - they fainted a retreat and then slaughtered the pursuing English.
The Normans won and took over the whole of the land and changed England forever. A new language was created, a pidgin composed of Old English and French and Latin and a smattering of other languages (thanks to the international coalition William had put together).
At any rate this research paper suggests King Harold backed the wrong man for Pope and so the Pope (Alexander II) backed Prince William in his bid to conquer England. It's why William was able to recruit so many lesser nobles all over the Continent to his cause; it was blessed by the Holy Father in Rome.
Read my rather lengthy but entertaining blogpost on Hastings here.