The Master of the Straits, called Elder Brother by sailors, is the son of the angel Rahab and a D'Angeline woman he kidnapped and took to the Three Sisters.
The Master of the Straits rules the waters between Terre d'Ange and Alba and Eire from the Three Sisters. For many years, he kept the nations from trading or allying with each other by forbidding passage, though he was known to let Thelesis de Mornay pass in her exile in exchange for a song. His mother singing to him is the only kindness he remembers. He possesses a sea mirror in which he can see all of Terre d'Ange and Alba.
In Kushiel's Dart
The Master of the Straits allowed an Alban delegation to cross, including Drustan mab Necthana, the Cruarch, and the Cruarch's wife Foclaidha because of a prophecy stating that his freedom would come when the two nations were united in marriage. Quintilius Rousse tried to send the message that "when the black boar rules in Alba, Elder Brother will accede" to Anafiel Delaunay de Montrève, who was working on the puzzle of the Master of the Straits, but Delanuay was killed before the message could be delivered.
Later, Phèdre nó Delaunay, Joscelin Verreuil, Quintilius Rousse, and Hyacinthe sought passage across the straits. The Master of the Straits let them pass when Phèdre sang Skaldi hearth songs. Yet on their way back, also bringing Alban soldiers to fight the Skaldi about to invade Terre d'Ange, a sailor caused offense by fishing in the Master of the Straits' waters, and the Master of the Straits brought them all to the Three Sisters and summoned Phèdre, Drustan, Quintilius, and Hyacinthe ashore. Joscelin, as Phèdre's sworn companion, asked to come with.
One ashore, the Master of the Straits told them that the marriage between Drustan and Ysandre de la Courcel is only half of what binds him to the island and immortality. The other half is up to them to guess in exchange for the party's freedom. He gives the hostages one night to think over the riddle.
Phèdre learns that the Master of the Straits's freedom comes at the price of someone else taking his place and so guesses when called before the Master of the Straits the next day. The Master of the Straits further asks the hostages to guess the source of his power. From her studies, Phèdre knows this is the lost book of Raziel and so guesses. Hyacinthe, not wanting Phèdre to be condemned to spend eternity on those islands, uses the dromonde to see backwards and elaborates on the answer. He says it is only pages from the book that give his power and that the book was given by the One God to Edom, the first man, to give him mastery over the earth and the sea, but that Edom disobeyed the One God, so he took the book away. These acts fulfilled the curse that Rahab placed on his son.
Hyacinthe then entered training to become the new Master of the Straits by learning to read from the lost book of Raziel. He was then doomed to age but live eternally, or until someone else came ashore to take his place.
In Kushiel's Avatar
Phèdre spent the next several years studing Yeshuite lore and history to learn how to free Hyacinthe and eventually learns that uttering the name of the One God will bind Rahab and break the curse. However, it was Melisande Shahrizai de la Courcel who learned the location of the lost tribe of Dan, believed to know the name of the One God. She provided this information to Phèdre for a price.
Phèdre frees Hyacinthe from his curse. Though he is no longer doomed to immortality, he maintains his power. His desire is to let the power die when he does and so asks Phèdre and Joscelin to hide the lost book of Raziel.