Aemon Targaryen was the third son of Prince Maekar, later King Maekar I, and grew up watching his family's throne consume its own — close enough to the Blackfyre wars and their aftermath to draw the obvious lesson early. Rather than wait his turn at a succession he had already watched turn men into killers of their own kin, he went to the Citadel and forged a maester's chain, an unusual road for a Targaryen prince and, by his own later account, the only decision of his life he never once regretted.
The crown found him anyway. When his father died in 233 AC, the Great Council convened to choose the next king offered it to Aemon first, as the eldest surviving son's line; he refused it in favor of his younger brother Aegon, later Aegon V, and asked only to be allowed to go on being a maester. The Citadel granted the request and, not long after, posted him to the one place in the Seven Kingdoms least interested in his birth: Castle Black, at the Wall's foot, where a Targaryen name bought him nothing and a maester's training bought him everything.
He served the Night's Watch for the rest of his long life — one hundred and two years by the count kept at Castle Black, which made him one of the oldest men in Westeros by the time Jon Snow arrived to take the black. Blind for decades before his death, he remained sharper than most sighted men the Watch could produce, and it was his counsel, not his blood, that the brothers of his order came to depend on. Sent south for his own safety in 300 AC with Samwell Tarly as his escort, he fell too ill on the crossing to go on, was nursed in Braavos rather than buried there, and died in his sleep on the onward leg toward Oldtown, off the coast of Dorne — his body kept in a cask of rum, since no ship's captain would allow a Targaryen's funeral pyre on deck, until it could be given the flame his birth had once promised him.