Faith of the Seven|
The World of Ice & Fire (mentioned)|
The Sons of the Dragon (mentioned)
Physically, Septon Moon was described as "a bearded brute" of a man.
Following the Faith Militant's defeats in 42 AC in the battles at Stonebridge and the Great Fork of the Blackwater, new leaders arose across the Seven Kingdoms in 43 AC. Among these were Ser Joffrey Doggett in the westerlands, Poxy Jeyne Poore in the Kingswood of the stormlands, and Septon Moon in the riverlands. Others included Dennis the Lame and Ragged Silas who, like Moon, were hardly distinguishable from outlaws.
No longer would the Faith Militant openly march to pitched battle against Maegor's armies, and risk destruction by the Targaryen dragons. Instead, these new leaders waged a guerrilla war against Maegor's forces across southern Westeros, roaming the woods and hedges and wild places and striking back where they could. Maegor put a bounty out on them, a gold dragon for the scalp of a Warrior's Son and a silver stag for the scalp of a Poor Fellow, to encourage men to hunt down the rebel bands. Many did, but more of the smallfolk rallied to their cause, hearing sermons from these persecuted holy men of the Faith, hiding them and giving them what supplies they could. Here and there pious lords would render them aid as well.
Septon Moon's outlaw band even "elected" him as their own High Septon, in defiance of the "High Lickspittle" that Maegor had forced the Most Devout in Oldtown to prop up as his puppet. In time, it appears that many of the Poor Fellows across Westeros came to regard him as the real High Septon. Moon came to roam at will around the southern riverlands and northern Reach, evading royal forces: whenever he emerged from the woods to preach, he drew huge crowds to hear his condemnations of Maegor.
Maegor marshalled his main army and launched a new major campaign against the Faith Militant in 45 AC, targeted at Poxy Jeyne Poore and her followers in the stormlands. This grueling campaign ended a year later with their destruction and her burning at the stake, but Maegor targeting his main focus against her relieved pressure off the other groups of the Faith Militant in the rest of Westeros, giving Doggett and Moon's followers a chance to recover.
In 47 AC, seeking to finally produce an heir, Maegor announced that he would simultaneously marry three new brides in a triple-wedding ceremony - who came to be known as his "black brides" because they were all widows of proven fertility: Jeyne Westerling, Elinor Costayne, and his own half-niece Rhaena Targaryen. None of the great lords of the realm dared raise objection, but Septon Moon appeared at the town of Stoney Sept to denounce Maegor's wedding plans, to the cheers of crowds numbering in the hundreds.
By 48 AC, Maegor's increasing brutality had finally alienated most of the great lords, following his execution of his wife Tyanna of the Tower for poisoning his other brides. Septon Moon appeared again, leading an army of thousands of Poor Fellows south through the Reach to Oldtown, with the openly announced intent of "bearding the Lickspittle in the Starry Sept", to demand that he lift the ban on the military orders and denounce Maegor, "the Abomination on the Iron Throne". When Lord Oakheart and Lord Rowan appeared before him with their own armies, they did not attack Septon Moon but joined their forces to his. Meanwhile, Joffrey Doggett was seen entering Riverrun - not as a captive or a besieger but as a guest of Lord Tully. Maegor's few remaining followers then abandoned him in rapid succession, and he was soon found dead on the Iron Throne itself.