He was born of the illicit union of Rhaegar Targaryen and Lyanna Stark, which was
either an elopement or an abduction, depending on who you ask. In any case, this union
provoked a rebellion that destroyed the Targaryen dynasty, killing Rhaegar, his father King
Aerys, and all of the rest of them save Viserys and the infant Danerys. Lyanna died giving birth
to him, after giving him to her brother Eddard Stark, Lord of Winterfell. To keep the boy safe
from the new dynasty, Eddard pretends that he is his own bastard son, and gives him the name
Jon Snow (Snow being the name that all bastards are given in the north). He grows up believing
he is an ill-gotten bastard, and endures a bastard's treatment at the hands of Eddard's wife
Catelyn (and to a lesser degree, their daughter Sansa).
He grows up without prospect, and casts his lot with the Night's Watch at the beginning
of the story, because in the Night's Watch, he thinks, a man can make his own name and his own
contribution. He accepts that he must swear to take no wife and own no lands and father no
children and die at his post at the Wall, guarding the realms of mean from wildlings (and the
Others, demonic beings of ice-magic who can raise and enslave the dead, whom no one believes
in anymore but who are, of course, completely real). He goes and does this, enduring contempt
from those who dislike his father or think him guilty of lording it over his fellows. He serves
through disappointment and hardship, but he takes his oath.
Elsewhere, Eddard Stark his killed by the machinations of the Lannister family, and his
son and heir Robb goes forth to avenge him. War breaks out from one end of the continent to
another, and still Jon Snow sits at his post, dreaming of being a ranger. Ironborn attack winter
fell and capture Bran and Rickon Stark, the youngest of the family, and still Jon does his duty,
forgoing his kinship and the home of his childhood. He does try to run away, but is stopped by
his comrades before a punishment is merited. He is, in the vicious vendettas of Westeros' morally
empty ruling class, a man fully noble.
He goes on a mission for the Night's Watch, to infiltrate the wildlings and learn of their
new King-Beyond-the-Wall. Jon does as he is bidden. He even pretends to betray the Watch, but
holds back at the last minute and returns to the Wall, in time to fight against the Wildling attack.
In the election for a new Lord Commander of the Night's Watch, Jon wins, largely by the
support of his friends. He did not seek the position, but bears its duties as best he may.
Percieving that the Others are real and the wildlings were merely trying to escape them, he offers
to settle them at the Wall, under Night's Watch governance, to unite agains the threat. He leads
an expedition to Hardhome beyond the Wall to rescue some more wildlings, and confronts the
Others, led by the fearsome Night King, for the first time. Horrified, he presses ahead with his
plans, and for his trouble, is assassinated by his fellows, who each say "for the Watch" as they
stab him.
He lays dead for a day, until Melisandre, by calling on R'hllor or some other magic,
revives him. He executes the traitors but then leaves the Watch behind (the oath was for life, and
he died). Here his half-sister Sansa re-enters his life, having escaped Lannister captivity and a
forced marriage to the wicked Ramsay Bolton, who holds Winterfell and his half-brother Rickon
Stark hostage. Jon gathers an army as best he is able, and with help from allies, defeats Ramsay