This page simply lists known Imperators and their Estates. Those with more complete descriptions elsewhere are linked.
Yama-Juei never calls his Chancel "Hades" or anything else some call it the Underworld, but Hades is the most popular name. Its importance is that it serves as a prison for Powers (and sometimes Imperators) who have been sentenced to some lasting punishment that is short of destruction. The Underworld has the unique property that once someone enters, no one may leave without Yama-Juei's consent not even a Noble or an Imperator. (Lord Entropy has never ventured into the Underworld, nor is he likely to. It is unknown whether an Execrucian could be trapped there.) Sometimes the Locust Court sentences a Noble to some period of torture and/or confinement in Yama-Juei's realm.
Yama-Juei is a True God. All of his Powers are themselves trapped in his realm, and suffer some perpetual torment. Yet they are powerful and capable of wielding their Estates outside their Chancel. Most are Immortal and/or Sacrosanct. Powers often come to Hades to ask one of Yama-Juei's Nobles for a favor. Of course, they do so with no guarantee either that they will be granted their favor, or be allowed to leave.
(As a practical matter, Yama-Juei will usually let visiting Powers leave, if they are polite, since holding them prisoner would irritate their Imperator, but he has been known to hold some captive for a long time, or simply make himself "unavailable," thus preventing visitors from being able to ask leave to depart).
The boatman Charon ferries souls across the River Styx, which runs along the perimeter of Hades. It is not known whether Charon is a Noble sentenced to ferry souls for all eternity, or whether he is some sort of spirit, or a magical Chancel resident. He does, however, have a high Auctoritas and the Sacrosanct gift it is a very foolish Power who tries to threaten him, or crosses the river by some means other than Charon's boat.
Yama-Juei's Powers are:
Sisyphus the selfsame Greek king of mythology is the Power of Futility, and he is a slave to his Estate, as he has been repeatedly rolling a boulder uphill only to see it slip and roll back down for millenia. He is a Regal, and being able to make any effort futile, or make a futile goal possible, brings many Nobles on an impossible quest to his hill in Hades.
The unfortunate Power of Hope is held prisoner in Hades, because were she to be allowed out, and possible destroyed by the Execrucians, it is doubtful that even the angels could bear the loss of Hope. (Certainly the Fallen could not.) Her Estate is attacked constantly, of course, but she defends against them well.
Iscarot, "the Hanged Man," is the Power of Prisons. Iscarot is not actually hung, but bound into the form of a tree standing alone on a hill not far from Sisyphus', where it is said that he suffers eternal pain akin to crucifixion. His is the power to make or unmake any prison. (Do not ask him to release you from Hades, however...)
Kevin is believed to be a True God, though he may be a Magister of the Wild. He is quite insane, but reasonably friendly (if he doesn't decide to disintegrate you with his gaze, something he can do through any Auctoritas).
Kevin is notable mostly because he rules the solar system in Prosaic reality, and so anyone traveling either through space, or to the nearby worlds on Yggdrasil in Mythic Reality, is likely to encounter his Child Soldiers; fearsome, almost indestructible warriors made from the souls of children, with black angels' wings and the ability to cast beams of destruction from their eyes similar to their god.
His Chancel is on one of the outer planets the precise location is not known (it may move), but to get there one must travel into space. Known gateways are in the asteroid belt, the rings of Saturn, and one of the moons of Jupiter. His Powers presumably have some way to get there even without a rocketship; they spend most of their time on Earth, but also a great deal of time out in space, defending against extraterrestrial threats.