- "When Aegon's heir wed his daughter to his son, the Faith could brook such abomination no longer. The High Septon led the denunciation of the Targaryens, and all over Westeros the Faith Militant took up its swords against the dynasty and its supporters."
- ―The High Sparrow
King Aegon the Conqueror had two children by his two sister-wives: his firstborn son Aenys with his sister Queen Rhaenys, and his second-born son Maegor with his sister Queen Visenya. When Aegon I eventually died, Aenys succeeded him as the second king on the Iron Throne.
The Conquest was still within living memory, however, and many still chafed under Targaryen rule - and saw the death of Aegon I as an opportunity to throw off their rule. Several localized rebellions therefore broke out at the beginning of Aensys's reign, such as the insurrection of the "Vulture King" in the Red Mountains along the border with independent Dorne, but these uprisings were ultimately put down - not really due to Aenys's leadership, but capable local rulers such as House Tarly, among others.
The Targaryens had incestuously married brother to sister for generations (whenever possible) to "keep the bloodline pure", in the custom of their Valyrian ancestors - which the Faith of the Seven in Westeros considered an abomination. For that matter, Aegon I broke not only the Faith's rules against incest, but its rules against polygamy, as he was married to both of his sisters at the same time.The Faith wasn't in much position to challenge the victorious Targaryen army after the Conquest, or their massive dragons, but Aegon I was wise enough to tread lightly with the Faith: both sides tacitly agreed that the Targaryens' incestuous marriages were a relic of their past, which would soon fade. Aegon I didn't intend for future generations of his new dynasty to continue to have incestuous marriages, and in return, the Faith didn't press the matter for the remainder of his life. Aegon I eventually died and was succeeded by his elder son, Aenys.
To the surprise of all, however, later in his reign King Aenys tactlessly wed his daughter to his own son: the incestuous marriage of Princess Rhaena and Prince Aegon broke the Targaryens' prior promise to the Faith, which could stand the abomination no longer. The new High Septon led the denunciation of the Targaryens, and the military order of the Faith of the Seven, the Faith Militant, rose up in open revolt.King Aenys proved to be an utter weakling in the face of the revolt and was completely overwhelmed. As the Faith Militant attacked lords that still supported him across the Seven Kingdoms, one particularly zealous force of the order even managed to scale the walls of the (still under construction) Red Keep, and would have killed Aenys and the royal family if not for the intervention of the Kingsguard. Frightened, Aenys fled King's Landing entirely and retreated to the Targaryen fortress-refuge at Dragonstone - where he soon died of cramps brought on from the stress.
Instead of his own children, Aenys was then succeeded by his younger half-brother Maegor, Aegon I's only child by Visenya. Maegor was his brother's exact opposite: a highly skilled warrior and brutal tyrant, quickly earning him the name "Maegor the Cruel".
Maegor ultimately died childless, however, and Aenys's youngest son succeeded to the throne as King Jaehaerys I: hence all subsequent Targaryen monarchs descended from Aenys, not Maegor.
Aenys's name is briefly seen on a page of the book "The Lineages and Histories of the Great Houses of the Seven Kingdoms" when Lord Eddard Stark is searching through it. On a page about House Baratheon, it is mentioned that one of Orys Baratheon's sons, a member of the Kingsguard, died thwarting an assassination attempt against Aenys.
|Aegon I Targaryen|
|Maegor I Targaryen|
|Jaehaerys I Targaryen|
In the books
In the A Song of Ice and Fire novels, Aenys was the first son of Aegon the Conqueror and Queen Rhaenys, before she died fighting in Dorne. Maegor, meanwhile, was the son and only child of Queen Visenya, Aegon's other sister-wife, making him Aenys's half-brother.
George R.R. Martin made Targaryen dynasty names by mix-and-matching different name elements: "Ae-" in "Aegon", "Aemon", "Aemond", "Aerion", etc., and the suffix "-nys" from "Rhaenys" (less clearly, "Viserys" and "Daenerys"). In-universe, Aenys's name is apparently simply a combination of his parents' names: "Ae-gon" and "Rhae-nys" yielded "Ae-nys". It is pronounced like both elements in his parents' names: "AY-nis", but not "Ay-nus".
Aenys was considered to be a weakling. He was as tall as his father but softer looking, slender and frail. He was very sickly as a child. His mother Rhaenys died when he was only three years old, which deeply traumatized him. He grew somewhat stronger and more confident after bonding to his dragon Quicksilver (progeny of the original three dragons brought to Westeros during the Conquest). Like his mother, Aenys enjoyed court life and was a great patron of the arts: he was dabbler in poetry and alchemy, though not much of an academic. Nonetheless he was quite charming on a personal level at court, in contrast with his brutish younger half-brother. He wore his hair long down to his shoulders, curled into ringlets and perfumed. He also had a thin silky moustache and beard, well-manicured to come to a fine point (described as a "Three Musketeers" look by Martin). He wore a large gold crown much bigger than his father's simple band of Valyrian steel interlaid with large square-cut rubies. Despite being a courtier, he was not very charismatic in times of actual crisis, as those around him became disgusted at his weak will and indecision. He had a nervous smile, as if anxious and eager to please those around him.
Aenys wasn't a completely foppish incompetent (this reputation became somewhat exaggerated over time): he did well enough at jousting and feats of arms not to embarrass himself, he wasn't just tripping over his sword, but he was only adequate - in contrast with the great legacy of his father. Aenys might have made a decent enough caretaker king if he had inherited the throne in a time of peace - he may not have been a great statesman but he wasn't outright insane (like Aerys II), a religious buffoon (like Baelor I), or a cruel tyrant (as Maegor later became). The Targaryen dynasty was still young, however, and needed a forceful king to cement its status - and Aenys failed to rise to the occasion.
Because Aegon I didn't want to antagonize the Faith, he tacitly agreed not to continue the Targaryen custom of incestous marriage. Combined with the fact that Aegon simply never produced any daughters, he made Aenys wed Alyssa Velaryon as a political marriage (she was still a cousin given that the Targaryens had frequently intermarried with the Velaryons, but cousin marriage isn't considered incest in Westeros). Aenys and Alyssa had three sons and two daughters, who in order were: Rhaena, Aegon, Viserys, Jaehaerys, and Alysanne. Their sixth and final child was a daughter named Vaella, but she died in the cradle.
The construction of the Red Keep took many years and Aegon I only lived to see the foundations set: instead he spent much of his long reign on royal progresses across Westeros with an itinerant court, knitting together his newly forged kingdom. He kept Aenys by his side at his mobile royal court, while Maegor stayed behind on Dragonstone.
After Aegon I died of a stroke in 37 AL, Aenys I succeeded him as the second king of the unified Seven Kingdoms, when he was 30 years old. Aenys's weak reign was pervasively troubled by rebellions. Aegon I had been a strong conqueror, but the new king was held to be a weakling, and the War of Conquest was still within living memory. Many felt that the time was ripe to throw off Targaryen rule before it became solidified. Upon Aegon I's death, four "false kings" immediately revolted in local independence movements. A man claiming to be a son of Harren the Black, calling himself "Harren the Red", staged an uprising at Harrenhal. He was joined by a woman who had been raped by the lord of Harrenhal who claimed the right of First Night. Their forces massacred everyone in Harrenhal, wiping out House Qoherys. In the south, the first Vulture King rose up in the Red Mountains of Dorne. In the Vale of Arryn to the east, Lord Arryn's younger brother deposed him and threw him out of the Moon Door, then rose in revolt against the Iron Throne. Maegor himself crushed the revolt in the Vale, riding his father's dragon Balerion the Black Dread. There was even a localized rebellion in the Iron Islands, led by a crazed Drowned Man priest who claimed to be a son of the Drowned God. Vickon Greyjoy's son Goren put down the rebellion, and in gratitude Aenys said he would grant him any gift it was within his power to grant. Goren Greyjoy shrewdly requested that he allow them to remove all of the Septons and Septs from the islands, and because he had given his word Aenys reluctantly agreed. The septs were not very numerous on the isles to begin with, given that most of the ironborn followed the Drowned God, but this still upset the Faith on general principle.
Aenys's bastard half-uncle Orys Baratheon had served as Hand of the King at the beginning of Aegon I's reign but had since left the office, and he died of his wounds successfully crushing the insurrection in the Red Mountains. Meanwhile, Aenys's original Hand, Alyn Stokeworth, died putting down the rebels in the Riverlands. Therefore, as a reward for his success in handling the rebellion in the Vale, Aenys named Maegor to fill the vacant office as his new Hand of the King.
Overall, Aenys was not an absentee-king, and he did try to address these rebellions - but he was determined to solve them through politics and negotiations, when the time had truly come for war. He refused to use the obvious advantage of the Targaryen dragons. In contrast, Aenys's bloodthirsty half-brother Maegor was a great warrior, and crushed the rebellions that his older brother could no longer control. Very quickly, many came to see Maegor as the real power behind the throne. For a few years, at least, the two brothers successfully ruled over the realm.
With Aegon I, Rhaenys, and Orys dead, Dowager Queen Visenya became the last of the Conquest-generation of Targaryens, and she did much to aid her son Maegor's rise in power. Aenys even gave Maegor the ancestral Valyrian steel sword of House Targaryen, Blackfyre, which had been carried by their father - openly acknowledging that Maegor was a better warrior than he ever was. Maegor was frustrated by his inability to produce an heir in his arranged marriage to the High Septon's niece, however, who would never grant him a separation - so Maegor polygamously took a second wife, angering the Faith so much that Aenys had to exile him to Pentos.
With Maegor gone, there was no pragmatic restraint on Aenys's poor decisions. Despite an already strained relationship with the Faith, after a few years Aenys foolishly announced the marriage of his daughter and eldest child Rhaena to his eldest son Aegon. No one knows why Aenys voluntarily made such a massive political blunder: by that point he had grown very out of touch and genuinely believed himself to be very popular with all the people of the realm, and some think that as the Red Keep's foundations rose in construction he started to develop aspirations about the glorious Targaryen legacy he would leave behind. Either way, this directly resulted in the outbreak of the Faith Militant uprising.
Aenys was physically and emotionally overwhelmed by the rebellion, and fled King's Landing entirely to withdraw to Dragonstone. Aenys always had frail health, and the stress of the situation left him nearly catatonic, suffering from loose bowels and cramps. Visenya offered to help treat him, and for a time his health seemed to be improving - but then he collapsed when he heard that his children Rhaena and Aegon were besieged at Crakehall in the Westerlands: three days later he died. Some suspect that Visenya poisoned Aenys, as she had always pushed to further her own son Maegor over him his entire life and it was bizarre that she would volunteer to help heal him. Even those who suspect this debate her motivations: whether it was simply to advance Maegor, or because Aenys had proved himself such an incompetent (sparking the rebellion, losing King's Landing, then falling catatonic from the stress when he was needed the most) that she felt he needed to be removed for the good of the dynasty. Others point out that Aenys always had frail health, seemed to actually be improving for a time, and that the shock of learning that his two eldest children were besieged may simply have been enough to kill him.
Whatever the case, barely an hour after Aenys's body was cremated, Visenya flew to Pentos on Vhagar to retrieve Maegor, who flew back with her to Westeros riding Balerion. Maegor immediately usurped the throne ahead of Aenys's five children, but promptly regained control of King's Landing and started brutally hammering the Faith Militant.
After Maegor eventually died, he was succeeded by Aenys's last remaining son, Jaehaerys I. Thus all subsequent Targaryens (including Daenerys Targaryen) descend from Aenys and not Maegor. Aenys was remembered as a generally weak king, so no subsequent generations of the Targaryens ever named a son "Aenys" again (much as the name "Maegor" was avoided as well, for his legacy as a brutal tyrant).