The Helmet of Hades is a magic helmet that belongs to the god Hades. It is a symbol of his power, and a lot of his power comes from it.
The helmet's powers are giving its wearer the power of invisibility, and allowing a ghost to be brought back to life. Gods can become ivisible without the helmet, but this gives them a stronger form of ivisibility where even god can't see whoever is wearing it, and they are harder to sense. Their voice also echos aroun the area with it instead of coming from one spot. It also gives the user some power over the Underworld.
The helmet was first seen in Mortal Beloved where it was stolen by a dead serial murderer named Atyminius. He used to to take over the Underowlord, become invisible, and come back to life until Xena killed him. She and Marcus brought the helmet back to Hades.
It was seen last in Looking Death in the Eye when Hades tried to sneak up on Xena and Gabrielle. Xena then destroyed it with her chakram. It exploded, and it's sparks were even able to hurt the gods. After it was destroyed though, Hades wasn't as weakened as he was when it was stolen from him in Mortal Beloved.