Jon Snow might be one of the central figures of the story of Game of Thrones, and he just might be the most heroic character in the entire series, but just as with any adaptation from book to screen, many of the details behind Jon's characterization were lost in translation.
Game of Thrones captured the essence of Jon as a character, but A Song of Ice and Fire is full of little details that really flesh out his character further. So what do fans of George R.R. Martin's book series know about Jon that show fans wouldn't?
He Was Possibly Expected To Be A Girl
Rhaegar Targaryen is someone who is utterly obsessed with prophecies, and a big reason why he runs off with Lyanna and has Jon is because he believes he needs to have three children that are likely meant to mirror the original Targaryen conquerors, Aegon, Rhaenys, and Visenya.
His first two children are Aegon and Rhaenys, and he and Lyanna might have expected that Jon would be a girl in order to fully fulfill the prophecy and mimic the first Targaryen invaders.
He Has A Long Lost Brother
Although Rhaegar's first two children, Rhaenys and Aegon, are supposedly dead, there is a boy in Essos called Young Griff who believes that he's Aegon Targaryen. He has many Westerosi and Essosi supporters as well, and he's planning on invading Westeros soon.
If what Young Griff believes is actually true, then it would make Jon his younger half brother.
Catelyn Feels Threatened By Him
Jon and Cat don't interact much in the TV series, but it is clear that Cat can't stand him. However it's not entirely clear why.
It's true that Cat is jealous that Ned was with another woman, but the bigger issue in the books is that essentially Jon's existence and acknowledgement as Ned's son threatens the potential inheritance of her own children in the future if Jon tried to press his claim as a Stark.
Young Jon Fantasized About Being A Conqueror
The books unsurprisingly drop many hints and subtextual clues about Jon's Targaryen lineage, but one of the most obvious connections he bears with the Targaryens is that, at least when he was young, he dreamed of being a conqueror like the Targaryens.
He took a particular interest in King Daeron Targaryen, a young Targaryen that managed to conquer the ever-rebellious kingdom of Dorne (even though he didn't hold it for long).
Someone Who Knows His Parentage Is Still Alive
Jojen and Meera Reed were significant characters on Game of Thrones, but one potentially very important character in the books was only seen once in a flashback on the show.
Howland Reed, father of Jojen and Meera, is the only living person who actually knows who Jon is, he was with Ned at the Tower of Joy so is likely the key witness who can actually prove that Jon is actually the son of Rhaegar and Lyanna.
He Saved The Direwolves
This is obviously an element of the books that was kept for the series, but some of the deeper meaning behind it wasn't made clear.
When everyone finds the direwolf pups in the woods, Ned wants to give them a quick death. Jon intervenes and asks his father to reconsider, pointing out that there is one puppy for each of Ned's trueborn children. Ned gives in because Jon is being selfless and excluding himself as a Stark in order to save the pups.
He Looks A Lot Like Ned
Although Jon in the TV series has fairly quintessentially Stark looks, Sean Bean and Kit Harington don't look particularly alike.
However in the books, Jon and Ned look similar enough that most people presume that Jon doesn't take after his mother at all and solely takes after his father. In a roundabout way that's obviously still true in the show, given that he looks nothing like a Targaryen, but he still doesn't look much like TV Ned either.
He's One Of The Only Stark Children Who Looks Like A Stark
Despite the fact that most of the Stark children on Game of Thrones seem to take after the typical Stark looks as opposed to Catelyn's classic Tully looks (with the obvious exception of Sansa), in the books it's the opposite.
Nearly all of Ned's children with the exception of Jon and Arya look more like Catelyn than they do like Ned, a contrast that seems to be irksome to Catelyn in particular.
He Died Trying To Save Arya
Jon was murdered by a man of the Night's Watch at the end of the last released book, but the buildup to it is quite different. In the books, Ramsay Bolton has married someone that he is claiming is Arya Stark.
After receiving a threat that seems to come from Ramsay, Jon decides to leave the Night's Watch and go south in order to rescue his little sister, and he's killed as a result of that instead of dying for saving the wildlings.
He'll Likely Warg Into Ghost
The show really only delved into the idea of Bran Stark as a warg, however there are very obvious indications that all of the Stark children can and occasionally do subconsciously warg into their wolves.
It won't be confirmed until the next book is released, however a key aspect of Jon's death and resurrection will likely be tied to Ghost, and it seems probable that he has warged into Ghost when he was killed.