Hades' Helm, also known as the Helm of Darkness or the Cap of Hades, was one of the main weapons that Hades had.
Also known as the Helmet of Invisibility, the Helm was created by the Cyclopes and was given to Hades as a gift after his brother, Zeus, freed them from Tartarus. Those same Cyclopes also forged the Lightning of Zeus and Poseidon's Trident, also as gifts for their freedom.
In Multiplayer, there were two of Hades' Helms.
An item named Hades' Helm was the first one to be available for Hades' Warriors. When used, its owner evaded an attack and became invisible to all the other players for a limited period. It caused the screen screen to glow Purple when activated and it kept flashing in purple as long as the invisibility lasted. Like all the other items of Multiplayer, it could be leveled up to Level 3 to increase its effect duration and decrease its cool down period.
The Helmet of the Battle Armor of Hades was the one worn by Hades in God of War III, which kept its horns and even its orange fiery glow.
Perseus used a magic helm in his battle against Kratos. As he put it on his head, Perseus turned invisible, and took advantage of that in his fight against the Spartan, who could only see Perseus' position by looking at his steps in the water.
After weakening Perseus in his invisible form, Kratos lifted him by holding his neck and stepped on the helmet, which destroyed it. Then, he threw Perseus back to the ground and continued their fight.
Hades wore a horned helm that covered his whole face and from which flames came out. Although that Helm couldn't turn him invisible, apparently (otherwise he would have used such ability against Kratos) Hades did turn invisible when Kratos entered the statue as he was nowhere to be seen, it was an important and powerful piece of armor.
For being worn by Hades for so long, it seemed to have become even part of his body, which caused him great pain if it was removed and even ripped some of his skin with it. Another hypothesis was that the reason that Hades' face was so deformed was because of the digestion that he suffered in his childhood inside of Cronos' stomach, and that the Helm would have only helped hide his face's deformed condition.
During Kratos' fight with Hades, Kratos slammed Hades' head on Hades' Throne Room's ceiling many times, which caused him to fall into River Styx and granted Kratos the Claws of Hades, which were Hades' weapon of choice in the game. Moments later, Hades emerged from the River Styx in his giant form without his Helm and was ultimately killed by Kratos.
After that fearsome battle, the Helm could be retrieved as one of Ten Godly Possessions of the game: it could be acquired by swimming to the bottom of River Styx, before using the River to leave to the next room. Since the bottom of the River was very bright and the Helm was made of dark Bronze, it's fairly easy to spot. It also kept its trademark orange glow, which made it even easier to be seen. It's needed to swim constantly against the River's currents in order to get to it, or Kratos simply used a Swim Dash.
Equipping the Helm during Bonus Play maxed out Kratos' heath, magic, and item bars, without the need to collect Gorgon Eyes, Phoenix Feathers,or Minotaur Horns throughout the game in order to do so. Like all of the Godly Possessions, it disabled Trophies as soon as it's turned "on".
- In Greek Mythology, that Helm was given (or lent) to Perseus by Hades in order to kill Medusa, when he was challenged by the King of his island to do so, but since Medusa wasn't killed by him in God of War, the reasons why he received such a helm were unknown.
- A second hypothesis was that, in the God of War Series, it was given to Perseus by the Gods to kill Kratos or simply to conclude his journey to the Sisters of Fate.
- A third hypothesis was that Perseus would have actually killed Medusa in the God of War Series and that she was simply resurrected by Ares in God of War and then killed by Kratos. The fact that a great part of Ares' Army in that game was made of Undead Warriors supported that idea.
- It was explicit that, in the God of War Series, there were at least two of Hades' Helms: the one that Perseus used and the one that Hades worn. The reason why the weakest one (with less magic abilities) was in Hades' possession was unknown. Possibly, it was to benefit gameplay and make Perseus' and Hades' respective characters and their original mythological versions more alike.
- In God of War: Ascension, however, the helm that the warriors used as an item did seem to be Hades', and not the one that Perseus had. That confusing statement may have indicated that the Helm that Hades worn in God of War III actually could made its owner invisible, but such an ability was never used by Hades in the God of War Series.