In Greek mythology, the Cap of Invisibility (aidos kyneê in Greek) is a mysterious helmet or cap that possesses the ability to turn the wearer invisible. Also known as the Cap of Hades or Helm of Hades It was used by numerous figures, including the goddess of wisdom, Athena, the messenger god, Hermes, and the hero, Perseus. The Cap of Invisibility is said to enable the user to hide from the eyes of other supernatural beings, functioning much like the cloud or mist that the gods surround themselves in to become undetectable
According to the mythographer Apollodoros, the Cap of Invisibility (among other items) was created by the Cyclops during the War of the Titans (Titanomachy). The Cyclops gave the thunderbolt to Zeus, the trident to Poseidon, and the Cap of Invisibility to Hades Other than this, however, it was never said that Hades ever used the Cap of Invisibility, nor was it said that any of the users of the Cap ever borrowed it directly from him.
The goddess of wisdom, Athena, used the Cap of Invisibility in one instance during the Trojan War. She used it to become invisible to Ares when she aided Diomedes, his enemy. Her assistance even enabled Diomedes to injure the god of war with a spear.
The messenger god, Hermes, wore the Cap during his battle with Hippolytos, the giant.
In some stories, Perseus received the Cap of Invisibility (along with the Winged Sandals and a special pouch) from Hermes when he went to slay the Gorgon Medusa. In other myths, however, Perseus obtained these items from the Stygian nymphs. The Cap of Invisibility was not used to avoid the Gorgons' petrifying gazes, but rather to escape them later on after he had decapitated Medusa's head.