Since we are collecting all the top theories here, I thought I'd drop this one I found that's going viral on the web. It's the first comment on this Youtube video by user Bael Bard: youtube.com/watch?v=O3o2LqFZcGU. Funnily, it was posted 2 years ago! Here's the theory:
Rhaegar is Azor Ahai. Jon Snow is Lightbringer aka The Prince That Was Promised. There were three attempts to create the sword according to legend. " He labored for thirty days and thirty nights until it was done. However, when he went to temper it in water, the sword broke. The second time he took fifty days and fifty nights to make the sword, even better than the first. To temper it this time, he captured a lion and drove the sword into its heart, but once more the steel shattered. The third time, with a heavy heart, for he knew before hand what he must do to finish the blade, he worked for a hundred days and nights until it was finished. This time, he called for his wife, Nissa Nissa, and asked her to bare her breast. He drove his sword into her breast, her soul combining with the steel of the sword, creating Lightbringer" Here is three attempts:
- Aemon said, that at first Rhaegar thought he is the prince that was promiced. He died at the Trident. "When he went to temper it in water, the sword broke".
- Later he started to think his son Aegon is the one. But Aegon was murdered under Tywin's orders, who wanted revenge on Aerys. Lion's heart.
- After Azor Ahai (Rhaegar) pierced Nissa-Nissa (Lyanna) with his sword true Lightbringer was created. It killed Lyanna but her blood, her soul and her strength went into the stell.... Lightbringer is Lyanna's son - Jon Snow. He is The Prince That Was Promised and his song is The Song of Ice and Fire. And Azor Ahai is nothing more than his father.