A three headed hound named Cerberus.
hades
Yes... beasts, monsters, and the undead
Hades had his own realm of which he was King, that of the Underworld, and Hades did not often leave it.
shadow
hades power is to rule the underworld and he has it as his own rule
Hades himself owns a beast; guard dog named Cerberus. And I am sure The Underworld contains many countless unusual beings.
A dorky kid who turns out to be the powerful son of Hades
Hellhounds, Medusa, and Hades (technically, he is not a monster, he is a god)
The Titans? Like, Kronos (Zeus, Posiedon, and Hades dad)?
Zeus, Hades, and Poseidon, or the Big Three, swore on the River Styx, to no longer have demigod children, so when Zeus had Thalia, he broke his promise. Hades, angered that he broke his promise, sent horrible monsters after her.
Hades is married to His own neice, and His brother Zeus is also His Father-in-law.
The Underworld, where Persephone is Queen, is the House of Hades - where the dead souls dwell, and where monsters abide.