Differences between Show & Books about the Night's King:
- According to show, Night's King was a man captured most likely during First Men-Children of the Forest war. He was magically transformed into a "White Walker" by COTF to be used as weapon against onslaught of the First Men against the Old Races. By this we can assume that he lived at least 4000 years before the Night's King of the books. (First Men invaded Westeros 12,000 years before Aegon's conquest. Night's King lived in circa 8,000 BC (Before Conquest)).
- He has not died since the Long Night and has been leading the Others ever since.
- He is the first of his kind.
- He shows super natural abilities like causing fissures in ground, resurrecting the dead to turn them into Wights, breaking weapons with touch etc.
- According to Books, Night's King was a legendary Lord commander of the Night's Watch. He was 13th Lord commander of the Night's Watch. We do not have his name or House but Old Nan believes he was a Stark named Brandon, Brother to King in The North. Other people speculate that he was either a Bolton, Flint, Umber, Norrey or Woodfoot. We can however safely assume that he was one of the First Men because he lived in the Age of Heroes, Prior to Andal Invasions or Rhoynar Landings.
There's a debate whether he ever existed at all. That is the same case as other Legendary figures of the Age of Heroes such as Lann the Clever, Brandon the Builder, Durran Godsgrief etc. Quoting GRRM:
.. in the books he is a legendary figure, akin to Lann the Clever and
Brandon the Builder, and no more likely to have survived to the
present day than they have.
He was most certainly not the first one of the Others. Others existed before him which is evident because he took one of them for his bride. It was that woman who took his heart and soul and made him what he was.
- He might not have even been one of the Others at all. At least during the day light he could live as a man (Something which has never been said about the Others. Skin Changing is a gift of Old Races and the First Men). We do not know if he actually changed his form to one of the Others at Night. From Bran's POV:
Night's King was only a man by light of day, Old Nan would always
say, but the night was his to rule.
- He may have been killed after he was defeated in battle by combined Forces of King in the North and King Beyond the wall who were horrified by his acts. But we do not know that for sure but we do know that he lost the battle and his name and existence was wiped out from all records at command of the Victorious Kings.
- We do not know if he had any super natural powers. We are only told about his horrific acts without telling us what exactly were those acts. One of those is mentioned that he used to make sacrifices to Others, much like Craster does.
Yes, Show's Take on origin of the Night's King is deviating from the Book.
- In books, he is a man of the Night's Watch and possibly a Prince of the North. In show he is just a captive from Invading bands of First Men.
- In books he is only accused of making love, sacrifices to others and
some other atrocities but nothing suggests he was ever more than a
man. In show he is a super-natural being; immortal and magical.
- In show he is the First of the Others. In books he may not have been one of them at all, let alone the First.
- In show he is leader of the others. In books he made sacrifices to them which is synonymous to accepting their superiority.
- There's also chronological inconsistency between the time the Character is supposed to have originated in the show and in the books. According to show that Character lived a long time ago before he ever appeared in books.
The only connection is that both show and Books agree he was one of the First men.
It is also unlikely that he somehow escaped in the Books. He was surrounded on Both sides of the Wall by forces of King in the North and King beyond the Wall who had allied together to cast him down. Not to mention he was a man who was said to have known no fear so I doubt he made any attempt to escape into Northern Wilderness beyond the wall. (He took an Other as bride, how many men can say that?).
"He had been the thirteenth man to lead the Night's Watch, she said; a
warrior who knew no fear. 'And that was the fault in him,' she would
add, 'for all men must know fear." - Bran reflecting Old Nan's
Or it could be that he may have had a worst fate than death (Spoilers ahead, do not click if you do not want to be spoiled).