Harald Hardrada, Harold Godwin and William of Normandy all believed they had a claim to the English throne. It is questionable whether Harald Hardrada had a justifiable claim this will be explored in detail below.
In 1066 King Edward the Confessor died childless leaving England without an Heir. Harald Hardrada claim was based on his Viking heritage. Harold Godwin claim was based on coming from a powerful English family and William of Normandy's claim was based on a promise by Edward. These claims were influential on the final outcome.
Harald Hardrada was a Viking leader. He was a very powerful man and he believed he deserved to be to be the king of England because he was a descendant of King Canute who ruled England between 1016-1032. Also his family was promised they could have England which made him think he had every right to invade England and become king. This wasn't a very strong argument because he had hoped that his reputation of been a fierce fighter would be enough to claim England for his own.
Harold Godwin was Edward the confessor brother-in-law and the son of Earl Godwinson who was the most powerful noble in England. His claim to the throne was that he was already very much in control of England and on Edward's death bed Edward said to him “I commend my wife and my kingdom to your care” If this was true it would mean that he did have a rightful claim as it was the kings dying wish but the problem was that his sister was present and he rushed to be crowned kings so he could have had something to hide.
William of Normandy was the cousin of Edward the confessor. William's claim was that Edward promised him the throne after he sheltered Edward and protected his family until he was crowned. He also claimed that Harold Godwin had sworn him an oath of alliance. The problem with his claim was that Norman sources say that Edward forced Harold to swear an oath of alliance.
From the evidence Harald Hardrada was the least eligible person to claim the throne because his only claim was his relation to King Canute who had ruled England until Edward the confessor had stolen the throne.
King Knud of Denmark who ruled England from 1016 till 1035 influenced England for good.
The pronouns like THEY, THEM, THEIR, THERE and the verb TO TAKE all come from the Danish Vikings with all the numerous words like EGG, BIRD, KNIFE, HUSBAND, SISTER,WIFE and verbs like
TO GET,TO GIVE,TO GO and so forth.
The judicial system and many forms of government all come from the Danish Vikings.
William's claim is not valid as there is NO WAY of verifying the truth of his claim. And Anglo-Saxon king Harold's claim is partly valid because he was of Danish descent.