Drowned God

The Drowned God is the deity worshipped on the Iron Islands. Together with the North, where the worship of the Old Gods of the Forest remains strong, the Iron Islands is one of the few regions in Westeros not abiding by the main religion of the Seven Kingdoms, the Faith of the Seven.

Beliefs
The belief system of the Drowned God largely justifies the piratical and raiding lifestyle of the Ironborn. Much of the religion centers around maritime skills and seafaring ability. It is not simply praiseworthy to kill enemies in battle, it is considered a pious act. A youth in the Iron Islands is not considered a man until he has killed his first enemy. The religion also encourages paying the "iron price" instead of the "gold price" -- that is, it is better not to pay money for things, but to rip them out of the hands of dead enemies.

Surprisingly, while to outsiders the Drowned God religion seems like a thinly veiled justification for pillaging and plundering, the Ironborn themselves take their religion very seriously, and actually have a fairly well developed cosmology and belief system surrounding it.

Within this belief system, the Drowned God is locked in an age-old struggle against the Storm God. The Drowned God's halls are located beneath the ocean, while the Storm God lives in the sky with his thunderclouds. The Storm God is constantly trying to send storms to dash Ironborn ships against rocks to their ruin.

Due to their belief, the ironborn do not fear drowning in the sea. "Godly" ironborn, that is fearless raiders, who drown are believed to be taken to the Drowned God's watery halls to feast on fish and be tended by mermaids.

Practices
The common prayer exchanged by followers of the Drowned God is "What is dead may never die", with the responding line, "But rises again, harder and stronger". If one person begins this prayer, others are usually expected to join in. The prayer involves clutching the right hand in a fist over the heart.

Priests of the Drowned God are called Drowned Men. They anoint devotees using sea water, which is considered to be holy water in the religion. Infants are ceremonially "drowned" during a baptism rite by being briefly submerged in sea water, or by a priest pouring sea water over their head. Adults may also be anointed with sea water in this fashion, when receiving a blessing from one of the Drowned Men.

"-Let [name] your servant be born again from the sea, as you were. Bless him with salt, bless him with stone, bless him with steel. -What is dead may never die. -What is dead may never die, but rises again, harder and stronger""

The Drowned Men themselves become priests by being "drowned" a second time, this time for real by being forcibly held under the waves by current priests (the name "drowned men" is quite literal). After their lungs fill up with water and they stop moving, they are brought back to shore, and revived by a priest using a crude form of CPR. If he is successfully revived, the gathered Drowned Men welcome their new brother to the clergy. The Drowned Men are not always successful in reviving adherents, however, and a Drowned Man is considered to be very holy indeed if he has failed to revive only one or two men who undergo the ceremony in his career.

Unlike the Faith of the Seven or the worship of R'hllor, the Drowned God religion is somewhat misogynistic: Ironborn men are expected to raid, plunder, kill, and command ships, but it is frowned upon for Ironborn women to do any of these things. While the Faith of the Seven and R'hllor have female priests (and the Old Gods of the Forest simply have no priests), the Drowned God's priesthood is all-male.

It is thus considered quite unusual that Yara Greyjoy, as a young woman, has risen to command her own ship and led men on raids. Further, it is a testament to her popularity with the Ironborn men she commands that they would willingly follow her, as she would have to work even harder and be a very capable commander indeed to earn the respect of such men. Despite being a very devout and pious follower of the Drowned God, even Balon Greyjoy himself is proud of and accepts Yara's activities, which are decidedly unorthodox for a woman in his culture.

In the books
The Drowned Men priesthood have no higher level of organization. Apparently, any priest may initiate another man as a priest. As for how they maintain standards in this situation, presumably if a priest isn't acting very godly, he will be killed by the other Drowned Men for his sacrilege. During the time of the War of the Five Kings, at least, Aeron "Damphair" Greyjoy is universally held to be the leader of the Drowned Men, who obey his orders without question, and he commands great respect from all of the Ironborn. However, Aeron wasn't appointed to some sort of position of high priest; rather is seems that he rose to a position of primus inter pares through general acclamation.