The hype over Jon Snow’s true parentage has been something fans have expressed for a long time as they waited for it to be revealed. So when Rhaegar Targaryen and Lyanna Stark’s relationship was finally shown in the Game of Thrones Season 7 finale, it was a long time coming. Viewers also got to learn that Jon’s name was meant to be something else entirely — a name that holds much more importance to the Targaryen family tree: Aegon. So, who is Jon Snow named after on Game of Thrones?
The meaning behind his birth name, Aegon Targaryen, has a lot to do with his birth father Rhaegar, and in some ways, his tragic past with the Houses of Lannister and Baratheon. Fans now know that Jon Snow’s real name is Aegon, but it’s curiously a name shared with Rhaegar and Elia Martell’s dead infant son, who was a victim of Gregor Clegane, a.k.a. The Mountain, during Robert's Rebellion. In the books, Tywin Lannister ordered the murder of Elia and her small children, Aegon who was an infant, and Rhaenys who wasn’t much older.
Because murdering Elia and her two heirs to the Iron Throne were in the best interest of helping to secure Robert’s place as the new king of Westeros, Tywin had The Mountain do it for him out of loyalty to Robert and in the hopes that he could merge House Lannister with House Baratheon, which as fans know, he eventually did by way of a marriage between Robert and Cersei.
For those who are strictly show watchers, you might remember Oberyn Martell, Elia’s brother, from back in Season 4 when he met his own death at the hands (literally) of The Mountain during a trial by combat on Game of Thrones. During the fight, Oberyn demanded that The Mountain admit his crimes that had happened prior to the events of the show. "Who gave you the order?" Oberyn shouted during the match. "Say her name! You raped her! You murdered her! You killed her children! Say it! Say her name!"
Finally, toward the end, when The Mountain was about to literally cave in Oberyn’s head, he yelled, "Elia Martell! I killed her children! Then I raped her! Then I smashed her head in like this!" And in the books, that’s pretty much what happened. He was ordered to kill Elia and her children, including Rhaegar’s son Aegon, and after he killed the children, he raped Elia before murdering her as well.
If it sounds brutal, that’s because it definitely was, but naming Jon after Aegon wasn’t necessarily to name his son with Lyanna after his dead infant, even though fans might at first be confused by his decision to double up on the name. You see, it's apparently a tradition in House Targaryen. In the family tree, there have been a number of men named Aegon and the first was Aegon the Conqueror, who was the first to conquer and rule Westeros. Most closely related to Rhaegar was his grandfather Aegon V, who was also the brother to Maester Aemon from Castle Black, who affectionately called Aegon "Egg."
It also brings more validity to Daenerys’ vision in the House of the Undying. On Game of Thrones, she had the vision when she was trying to find her dragons in the House of the Undying in Qarth back during Season 2, but in the book, there were more aspects to the vision. In A Clash of Kings, one of the visions shown to Daenerys in the House of the Undying is a silver-haired man thought to be her dead brother Rhaegar (Jon’s true father).
He stands holding a baby and says, "Aegon. What better name for a king?" A woman next to him, presumably Elia but now possibly Lyanna, replies, "Will you make a song for him?" Rhaegar then says, "He has a song. He is the prince that was promised, and his is the song of ice and fire. There must be one more. The dragon has three heads." Even though this may have just been a vision to tell Daenerys that there is a "prince that was promised," it could have also been showing her that, through ice and fire, Rhaegar's other son Aegon was born. In this case, that would now be Jon.
Knowing that Jon’s real name on Game of Thrones is the same of many other past characters might confuse some fans, but the good news is that all of the other Aegon Targaryens are dead, so if he wants to officially go by Aegon or even "Egg," he totally can.